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Wind

ContentsArticles

Wind engineering 1Wind tunnel 4Wind turbine 16Engineering 28Aerodynamics 38

ReferencesArticle Sources and Contributors 48Image Sources, Licenses and Contributors 50

Article LicensesLicense 52

Wind engineering 1

Wind engineeringWind engineering analyzes effects of wind in the natural and the built environment and studies the possibledamage, inconvenience or benefits which may result from wind. In the field of structural engineering it includesstrong winds, which may cause discomfort, as well as extreme winds, such as in a tornado, hurricane or heavy storm,which may cause widespread destruction. In the fields of wind energy and air pollution it also includes low andmoderate winds as these are relevant to electricity production resp. dispersion of contaminants.Wind engineering draws upon meteorology, fluid dynamics, mechanics, geographic information systems and anumber of specialist engineering disciplines including aerodynamics, and structural dynamics. The tools usedinclude atmospheric models, atmospheric boundary layer wind tunnels, open jet facilities and computational fluiddynamics models.Wind engineering involves, among other topics:•• Wind impact on structures (buildings, bridges, towers).•• Wind comfort near buildings.•• Effects of wind on the ventilation system in a building.•• Wind climate for wind energy.•• Air pollution near buildings.Wind engineering may be considered by structural engineers to be closely related to earthquake engineering andexplosion protection.

HistoryWind Engineering as a separate discipline can be traced to the UK in the 1960s, when informal meetings were heldat the National Physical Laboratory, the Building Research Establishment and elsewhere.

Wind loads on buildingsThe design of buildings must account for wind loads, and these are affected by wind shear. For engineeringpurposes, a power law wind speed profile may be defined as follows:

where:= speed of the wind at height = gradient wind at gradient height = exponential coefficient

Typically, buildings are designed to resist a strong wind with a very long return period, such as 50 years or more.The design wind speed is determined from historical records using extreme value theory to predict future extremewind speeds.

Wind engineering 2

Wind comfortThe advent of high rise tower blocks led to concerns regarding the wind nuisance caused by these buildings topedestrians in their vicinity.A number of wind comfort and wind danger criteria were developed from 1971, based on different pedestrianactivities such as:[1]

•• Sitting for a long period of time•• Sitting for a short period of time•• Strolling•• Walking fastOther criteria classified a wind environment as completely unacceptable or dangerous.Building geometries consisting of one and two rectangular buildings have a number of well-known effects:[2][3]

•• Corner streams, also known as corner jets, around the corners of buildings•• Through-flow, also known as a passage jet, in any passage through a building or small gap between two buildings

due to pressure short-circuiting•• Vortex shedding in the wake of buildingsFor more complex geometries, pedestrian wind comfort studies are required. These can use an appropriately scaledmodel in a boundary layer wind tunnel, or more recently there has been increased use of Computational FluidDynamics (CFD) techniques.[4] The pedestrian level wind speeds for a given exceedance probability are calculated toallow for regional wind speeds statistics.[5]

The vertical wind profile used in these studies varies according to the terrain in the vicinity of the buildings (which ismay differ by wind direction), and is often grouped in categories such as:[6]

•• Exposed open terrain with few or no obstructions and water surfaces at serviceability wind speeds.•• Water surfaces, open terrain, grassland with few, well-scattered obstructions having heights generally from 1.5 m

to 10m.•• Terrain with numerous closely spaced obstructions 3 m to 5 m high, such as areas of suburban housing.•• Terrain with numerous large, high (10 m to 30 m high) and closely spaced obstructions, such as large city centres

and well-developed industrial complexes.

Wind turbinesWind turbines are affected by wind shear. Vertical wind-speed profiles result in different wind speeds at the bladesnearest to the ground level compared to those at the top of blade travel, and this in turn affects the turbine operation.The wind gradient can create a large bending moment in the shaft of a two bladed turbine when the blades arevertical. The reduced wind gradient over water means shorter and less expensive wind turbine towers can be used inshallow seas.For wind turbine engineering, wind speed variation with height is often approximated using a power law:

where:

= velocity of the wind at height [m/s]= velocity of the wind at some reference height [m]

= Hellman exponent (aka power law exponent or shear exponent) (~= 1/7 in neutral flow, but can be >1)

Wind engineering 3

SignificanceThe knowledge of wind engineering is used to analyze and design all high rise buildings, cable suspension bridgesand cable-stayed bridges, electricity transmission towers and telecommunication towers and all other types of towersand chimneys. The wind load is the dominant load in the analysis of many tall buildings. So wind engineering isessential for the analysis and design of tall buildings. Again, wind load is a dominant load in the analysis and designof all long-span cable bridges.

References[1] Pedestrian wind comfort around buildings: comparison of wind comfort criteria. Table 3 (http:/ / sts. bwk. tue. nl/ urbanphysics/ pdf/

2013_BAE_WD_BB_TvH_Preprint. pdf)[2] Pedestrian wind comfort around buildings: comparison of wind comfort criteria. Figure 6 (http:/ / sts. bwk. tue. nl/ urbanphysics/ pdf/

2013_BAE_WD_BB_TvH_Preprint. pdf)[3] Wind Effects On Pedestrians. Figure 3 (http:/ / www. hkisc. org/ proceedings/ 2006421/ 6_Johnny_Yu Wind Effect on Pedestrians. pdf)[4] AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings (http:/ / www. aij. or. jp/ jpn/ publish/

cfdguide/ JWEIAguide. pdf)[5] Pedestrian Wind Environment Around Buildings. p112 (https:/ / www. cmff. hu/ oktatas/ tantargy/ NEPTUN/ BMEGEATMW08/

2010-2011-1/ ea_lecture/ blocken_pedestrianWindEnvironment. pdf)[6] AS/NZS 1170.2:2011 Structural Design Actions Part 2 - Wind actions. Section 4.2 (https:/ / law. resource. org/ pub/ nz/ ibr/ as-nzs. 1170. 2.

2011. pdf)

External links• International Association for Wind Engineering (http:/ / www. iawe. org/ )• American Association of Wind Engineering (http:/ / www. aawe. org/ )• UK Wind Engineering Society (http:/ / www. ukwes. bham. ac. uk/ )• World Wind Energy Association (http:/ / www. wwindea. org/ home/ index. php)

Wind tunnel 4

Wind tunnel

NASA wind tunnel with the model of a plane.

A model Cessna with helium-filled bubblesshowing pathlines of the wingtip vortices.

A wind tunnel is a tool used inaerodynamic research to study theeffects of air moving past solid objects.A wind tunnel consists of a tubularpassage with the object under testmounted in the middle. Air is made tomove past the object by a powerful fansystem or other means. The test object,often called a wind tunnel model isinstrumented with suitable sensors tomeasure aerodynamic forces, pressuredistribution, or otheraerodynamic-related characteristics.

The earliest wind tunnels wereinvented towards the end of the 19thcentury, in the early days of aeronauticresearch, when many attempted todevelop successful heavier-than-airflying machines. The wind tunnel wasenvisioned as a means of reversing theusual paradigm: instead of the airstanding still and an object moving atspeed through it, the same effect wouldbe obtained if the object stood still andthe air moved at speed past it. In thatway a stationary observer could studythe flying object in action, and couldmeasure the aerodynamic forces being imposed on it.The development of wind tunnels accompanied the development of the airplane. Large wind tunnels were builtduring the Second World War. Wind tunnel testing was considered of strategic importance during the Cold Wardevelopment of supersonic aircraft and missiles.Later on, wind tunnel study came into its own: the effects of wind on man made structures or objects needed to bestudied when buildings became tall enough to present large surfaces to the wind, and the resulting forces had to beresisted by the building's internal structure. Determining such forces was required before building codes couldspecify the required strength of such buildings and such tests continue to be used for large or unusual buildings.Still later, wind-tunnel testing was applied to automobiles, not so much to determine aerodynamic forces per se butmore to determine ways to reduce the power required to move the vehicle on roadways at a given speed. In thesestudies, the interaction between the road and the vehicle plays a significant role, and this interaction must be takeninto consideration when interpreting the test results. In an actual situation the roadway is moving relative to thevehicle but the air is stationary relative to the roadway, but in the wind tunnel the air is moving relative to theroadway, while the roadway is stationary relative to the test vehicle. Some automotive-test wind tunnels haveincorporated moving belts under the test vehicle in an effort to approximate the actual condition, and very similardevices are used in wind tunnel testing of aircraft take-off and landing configurations.

Wind tunnel 5

The advances in computational fluid dynamics (CFD) modelling on high speed digital computers has reduced thedemand for wind tunnel testing. However, CFD results are still not completely reliable and wind tunnels are used toverify the CFD computer codes.

Measurement of aerodynamic forcesAir velocity and pressures are measured in several ways in wind tunnels.Air velocity through the test section is determined by Bernoulli's principle. Measurement of the dynamic pressure,the static pressure, and (for compressible flow only) the temperature rise in the airflow. The direction of airflowaround a model can be determined by tufts of yarn attached to the aerodynamic surfaces. The direction of airflowapproaching a surface can be visualized by mounting threads in the airflow ahead of and aft of the test model. Smokeor bubbles of liquid can be introduced into the airflow upstream of the test model, and their path around the modelcan be photographed (see particle image velocimetry).Aerodynamic forces on the test model are usually measured with beam balances, connected to the test model withbeams,strings, or cables.The pressure distributions across the test model have historically been measured by drilling many small holes alongthe airflow path, and using multi-tube manometers to measure the pressure at each hole. Pressure distributions canmore conveniently be measured by the use of pressure-sensitive paint, in which higher local pressure is indicated bylowered fluorescence of the paint at that point. Pressure distributions can also be conveniently measured by the useof pressure-sensitive pressure belts, a recent development in which multiple ultra-miniaturized pressure sensormodules are integrated into a flexible strip. The strip is attached to the aerodynamic surface with tape, and it sendssignals depicting the pressure distribution along its surface.[1]

Pressure distributions on a test model can also be determined by performing a wake survey, in which either a singlepitot tube is used to obtain multiple readings downstream of the test model, or a multiple-tube manometer is mounteddownstream and all its readings are taken.It should be noted that the aerodynamic properties of an object can not all remain the same for a scaled model.[2]

However, by observing certain similarity rules, a very satisfactory correspondence between the aerodynamicpropertis of a scaled model and a full-size object can be achieved. The choice of similarity parameters depends onthe purpose of the test, but the most important conditions to satisfy are usually:•• Geometric similarity: all dimensions of the object must be proportionally scaled;• Mach number: the ratio of the airspeed to the speed of sound should be identical for the scaled model and the

actual object (it should be noted that having identical Mach number in a wind tunnel and around the actual objectis -not- equal to having identical airspeeds)

• Reynolds number: the ratio of inertial forces to viscous forces should be kept. This parameter is difficult to satisfywith a scaled model and has led to development of pressurized and cryogenic wind tunnels in which the viscosityof the working fluid can be greatly changed to compensate for the reduced scale of the model.

In certain particular test cases, other similarity parameters must be satisfied, such as e.g. Froude number.

Wind tunnel 6

History

OriginsEnglish military engineer and mathematician Benjamin Robins (1707–1751) invented a whirling arm apparatus todetermine drag and did some of the first experiments in aviation theory.Sir George Cayley (1773–1857) also used a whirling arm to measure the drag and lift of various airfoils. Hiswhirling arm was 5 feet (1.5 m) long and attained top speeds between 10 and 20 feet per second (3 to 6 m/s).However, the whirling arm does not produce a reliable flow of air impacting the test shape at a normal incidence.Centrifugal forces and the fact that the object is moving in its own wake mean that detailed examination of theairflow is difficult. Francis Herbert Wenham (1824–1908), a Council Member of the Aeronautical Society of GreatBritain, addressed these issues by inventing, designing and operating the first enclosed wind tunnel in 1871. Oncethis breakthrough had been achieved, detailed technical data was rapidly extracted by the use of this tool. Wenhamand his colleague Browning are credited with many fundamental discoveries, including the measurement of l/dratios, and the revelation of the beneficial effects of a high aspect ratio.Konstantin Tsiolkovsky built an open-section wind tunnel with a centrifugal blower in 1897, and determined thedrag coefficients of flat plates, cylinders and spheres.Danish inventor Poul la Cour applied wind tunnels in his process of developing and refining the technology of windturbines in the early 1890s.Carl Rickard Nyberg used a wind tunnel when designing his Flugan from 1897 and onwards.In a classic set of experiments, the Englishman Osborne Reynolds (1842–1912) of the University of Manchesterdemonstrated that the airflow pattern over a scale model would be the same for the full-scale vehicle if a certain flowparameter were the same in both cases. This factor, now known as the Reynolds number, is a basic parameter in thedescription of all fluid-flow situations, including the shapes of flow patterns, the ease of heat transfer, and the onsetof turbulence. This comprises the central scientific justification for the use of models in wind tunnels to simulatereal-life phenomena. However, there are limitations on conditions in which dynamic similarity is based upon theReynolds number alone.

Replica of the Wright brothers' wind tunnel.

The Wright brothers' use of a simple wind tunnel in1901 to study the effects of airflow over various shapeswhile developing their Wright Flyer was in some waysrevolutionary. It can be seen from the above, however,that they were simply using the accepted technology ofthe day, though this was not yet a common technologyin America.

In France, Gustave Eiffel (1832-1923) built his firstopen-return wind tunnel in 1909, powered by a 50 kWelectric motor, at Champs-de-Mars, near the foor of thetower that bears his name. Between 1909 and 1912Eiffel ran about 4000 tests in his wind tunnel, and hissystematic experimentation set new standards foraeronautical research. In 1912 Eiffel's laboratory wasmoved to Auteuil, a suburb of Paris, where his wind tunnel with a 2-metre test section is still operational today.Eiffel significantly improved the efficiency of

Wind tunnel 7

Eiffel's wind tunnels in the Auteuil laboratory

German aviation laboratory, 1935

the open-return wind tunnel by enclosing the testsection in a chamber, designing a flared inlet with ahoneycomb flow straightener and adding a diffuserbetween the test section and the fan located at thedownstream end of the diffuser; this was anarrangement followed by a number of wind tunnelslater built; in fact the open-return low speed windtunnel is often called the Eiffel-type wind tunnel.

Subsequent use of wind tunnels proliferated as thescience of aerodynamics and discipline of aeronauticalengineering were established and air travel and powerwere developed.The US Navy in 1916 built one of the largest windtunnels in the world at that time at the WashingtonNavy Yard. The inlet was almost 11 feet (3.4 m) indiameter and the discharge part was 7 feet (2.1 m) indiameter. A 500 hp electric motor drove the paddletype fan blades.[3]

Until World War Two, the world's largest wind tunnelwas built in 1932-1934 and located in a suburb of Paris,Chalais-Meudon, France. It was designed to test fullsize aircraft and had six large fans driven by highpowered electric motors.[4] The Chalais Meudon windtunnel was used by ONERA under the name S1Ch until1976, e.g. in the development of the Caravelle andConcorde airplanes. Today, this wind tunnel ispreserved as a national monument.

World War Two

In 1941 the US constructed one of the largest windtunnels at that time at Wright Field in Dayton, Ohio.This wind tunnel starts at 45 feet (14 m) and narrows to20 feet (6.1 m) in diameter. Two 40-foot (12 m) fanswere driven by a 40,000 hp electric motor. Large scaleaircraft models could be tested at air speeds of 400 mph(640 km/h).[5]

The wind tunnel used by German scientists at Peenemünde prior to and during WWII is an interesting example of thedifficulties associated with extending the useful range of large wind tunnels. It used some large natural caves whichwere increased in size by excavation and then sealed to store large volumes of air which could then be routedthrough the wind tunnels. This innovative approach allowed lab research in high-speed regimes and greatlyaccelerated the rate of advance of Germany's aeronautical engineering efforts. By the end of the war, Germany had atleast three different supersonic wind tunnels, with one capable of Mach 4.4 (heated) airflows.

A large wind tunnel under construction near Oetztal, Austria would have had two fans directly driven by two 50,000 horsepower hydraulic turbines. The installation was not completed by the end of the war and the dismantled equipment was shipped to Modane, France in 1946 where it was re-erected and is still operated there by the ONERA.

Wind tunnel 8

With its 8m test section and airspeed up to Mach 1 it is the largest transonic wind tunnel facility in the workld.[6]

By the end of World War Two, the US had built eight new wind tunnels, including the largest one in the world atMoffett Field near Sunnyvale, California, which was designed to test full size aircraft at speeds of less than250 mph[7] and a vertical wind tunnel at Wright Field, Ohio, where the wind stream is upwards for the testing ofmodels in spin situations and the concepts and engineering designs for the first primitive helicopters flown in theUS.[8]

Post World War TwoLater research into airflows near or above the speed of sound used a related approach. Metal pressure chambers wereused to store high-pressure air which was then accelerated through a nozzle designed to provide supersonic flow.The observation or instrumentation chamber ("test section") was then placed at the proper location in the throat ornozzle for the desired airspeed.In the United States, concern over the lagging of American research facilities compared to those built by theGermans lead to the Unitary Wind Tunnel Plan Act of 1949, which authorized expenditure to construct new windtunnels at universities and at military sites. Some German war-time wind tunnels were dismantled for shipment tothe United States as part of the plan to exploit German technology developments.[9]

For limited applications, Computational fluid dynamics (CFD) can increase or possibly replace the use of windtunnels. For example, the experimental rocket plane SpaceShipOne was designed without any use of wind tunnels.However, on one test, flight threads were attached to the surface of the wings, performing a wind tunnel type of testduring an actual flight in order to refine the computational model. Where external turbulent flow is present, CFD isnot practical due to limitations in present day computing resources. For example, an area that is still much toocomplex for the use of CFD is determining the effects of flow on and around structures, bridges, terrain, etc.

Preparing a model in the Kirsten Wind Tunnel, asubsonic wind tunnel at the University of

Washington

The most effective way to simulative external turbulent flow is throughthe use of a boundary layer wind tunnel.There are many applications for boundary layer wind tunnel modeling.For example, understanding the impact of wind on high-rise buildings,factories, bridges, etc. can help building designers construct a structurethat stands up to wind effects in the most efficient manner possible.Another significant application for boundary layer wind tunnelmodeling is for understanding exhaust gas dispersion patterns forhospitals, laboratories, and other emitting sources. Other examples ofboundary layer wind tunnel applications are assessments of pedestriancomfort and snow drifting. Wind tunnel modeling is accepted as amethod for aiding in Green building design. For instance, the use ofboundary layer wind tunnel modeling can be used as a credit forLeadership in Energy and Environmental Design (LEED) certificationthrough the U.S. Green Building Council.

Wind tunnel 9

Fan blades of Langley Research Center's 16 foot transonic windtunnel in 1990, before it was mothballed in 2004.

Wind tunnel tests in a boundary layer wind tunnelallow for the natural drag of the Earth's surface to besimulated. For accuracy, it is important to simulate themean wind speed profile and turbulence effects withinthe atmospheric boundary layer. Most codes andstandards recognize that wind tunnel testing canproduce reliable information for designers, especiallywhen their projects are in complex terrain or onexposed sites.In the USA many wind tunnels have beendecommissioned in the last 20 years, including somehistoric facilities. Pressure is brought to bear onremaining wind tunnels due to declining or erraticusage, high electricity costs, and in some cases the highvalue of the real estate upon which the facility sits. Onthe other hand CFD validation still requires wind-tunnel data, and this is likely to be the case for the foreseeablefuture. Studies have been done and others are under way to assess future military and commercial wind tunnel needs,but the outcome remains uncertain.[10] More recently an increasing use of jet-powered, instrumented unmannedvehicles ["research drones"] have replaced some of the traditional uses of wind tunnels.[11]

How it works

Six-element external balance below the KirstenWind Tunnel

Air is blown or sucked through a duct equipped with a viewing portand instrumentation where models or geometrical shapes are mountedfor study. Typically the air is moved through the tunnel using a seriesof fans. For very large wind tunnels several meters in diameter, asingle large fan is not practical, and so instead an array of multiple fansare used in parallel to provide sufficient airflow. Due to the sheervolume and speed of air movement required, the fans may be poweredby stationary turbofan engines rather than electric motors.

The airflow created by the fans that is entering the tunnel is itselfhighly turbulent due to the fan blade motion (when the fan is blowingair into the test section – when it is sucking air out of the test sectiondownstream, the fan-blade turbulence is not a factor), and so is notdirectly useful for accurate measurements. The air moving through thetunnel needs to be relatively turbulence-free and laminar. To correctthis problem, closely spaced vertical and horizontal air vanes are usedto smooth out the turbulent airflow before reaching the subject of thetesting.

Due to the effects of viscosity, the cross-section of a wind tunnel is typically circular rather than square, becausethere will be greater flow constriction in the corners of a square tunnel that can make the flow turbulent. A circulartunnel provides a smoother flow.

The inside facing of the tunnel is typically as smooth as possible, to reduce surface drag and turbulence that couldimpact the accuracy of the testing. Even smooth walls induce some drag into the airflow, and so the object beingtested is usually kept near the center of the tunnel, with an empty buffer zone between the object and the tunnelwalls. There are correction factors to relate wind tunnel test results to open-air results.

Wind tunnel 10

The lighting is usually embedded into the circular walls of the tunnel and shines in through windows. If the lightwere mounted on the inside surface of the tunnel in a conventional manner, the light bulb would generate turbulenceas the air blows around it. Similarly, observation is usually done through transparent portholes into the tunnel. Ratherthan simply being flat discs, these lighting and observation windows may be curved to match the cross-section of thetunnel and further reduce turbulence around the window.Various techniques are used to study the actual airflow around the geometry and compare it with theoretical results,which must also take into account the Reynolds number and Mach number for the regime of operation.

Pressure measurementsPressure across the surfaces of the model can be measured if the model includes pressure taps. This can be useful forpressure-dominated phenomena, but this only accounts for normal forces on the body.

Force and moment measurements

A typical lift coefficient versus angle of attackcurve.

With the model mounted on a force balance, one can measure lift, drag,lateral forces, yaw, roll, and pitching moments over a range of angle ofattack. This allows one to produce common curves such as liftcoefficient versus angle of attack (shown).

Note that the force balance itself creates drag and potential turbulencethat will affect the model and introduce errors into the measurements.The supporting structures are therefore typically smoothly shaped tominimize turbulence.

Flow visualization

Because air is transparent it is difficult to directly observe the airmovement itself. Instead, multiple methods of both quantitative and qualitative flow visualization methods have beendeveloped for testing in a wind tunnel.

Wind tunnel 11

Qualitative methods•• Smoke•• TuftsTufts are applied to a model and remain attached during testing. Tufts can be used to gauge air flow patterns andflow separation.

Compilation of images taken during an alpha run starting at 0 degrees alpha ranging to 26degrees alpha. Images taken at the Kirsten Wind Tunnel using fluorescent mini-tufts.

Notice how separation starts at the outboard wing and progresses inward. Notice also howthere is delayed separation aft of the nacelle.

Fluorescent mini-tufts attached to a wing in the Kirsten Wind Tunnel showing air flow directionand separation. Angle of attack ~ 12 degrees, speed ~120 Mph.

•• Evaporating suspensionsEvaporating suspensions are simply a mixture of some sort or fine powder, talc, or clay mixed into a liquid with alow latent heat of evaporation. When the wind is turned on the liquid quickly evaporates leaving behind the clay in apattern characteristic of the air flow.

Wind tunnel 12

China clay on a wing in the Kirsten Wind Tunnel showing reverse and span-wise flow.

•• OilWhen oil is applied to the model surface it can clearly show the transition from laminar to turbulent flow as well asflow separation.

Oil flow visible on a straight wing in the KirstenWind Tunnel. Trip dots can be seen near the

leading edge.

•• FogFog (usually from water particles) is created with an ultrasonic piezoelectric nebulizer. The fog is transported insidethe wind tunnel (preferably of the closed circuit & closed test section type). An electrically heated grid is insertedbefore the test section which evaporates the water particles at its vicinity thus forming fog sheets. The fog sheetsfunction as streamlines over the test model when illuminated by a light sheet.

Wind tunnel 13

Fog (water particle) wind tunnel visualization ofa NACA 4412 airfoil at a low-speed flow

(Re=20.000).

Video of a wind tunnel fog visualization [12]

•• SublimationIf the air movement in the tunnel is sufficiently non-turbulent, aparticle stream released into the airflow will not break up as the airmoves along, but stay together as a sharp thin line. Multiple particlestreams released from a grid of many nozzles can provide a dynamicthree-dimensional shape of the airflow around a body. As with theforce balance, these injection pipes and nozzles need to be shaped in amanner that minimizes the introduction of turbulent airflow into theairstream.

High-speed turbulence and vortices can be difficult to see directly, but strobe lights and film cameras or high-speeddigital cameras can help to capture events that are a blur to the naked eye.High-speed cameras are also required when the subject of the test is itself moving at high speed, such as an airplanepropeller. The camera can capture stop-motion images of how the blade cuts through the particulate streams and howvortices are generated along the trailing edges of the moving blade.

ClassificationThere are many different kinds of wind tunnels, an overview is given in the list below:•• Low-speed wind tunnel•• High-speed wind tunnel•• Supersonic wind tunnel•• Hypersonic wind tunnel•• Subsonic and transonic wind tunnelWind tunnels are also classified based on their main use.

Aeronautical wind tunnelsThe main subcategories in the aeronautical wind tunnels are

High Reynolds number tunnels

Reynolds number is one of the governing similarity parameters for the simulation of flow in a wind tunnel. For machnumber less than 0.3, it is the primary parameter that governs the flow characteristics. There are three main ways tosimulate high Reynolds number, since it is not practical to obtain full scale Reynolds number by use of a full scalevehicle.•• Pressurised tunnels - Here test gases are pressurised to increase the Reynolds number.• Heavy gas tunnels - Heavier gases like freon and R-134a are used as test gases. The transonic dynamics tunnel at

NASA Langley is an example of such a tunnel.• Cryogenic tunnels - Here test gas is cooled down to increase the Reynolds number. The European transonic wind

tunnel uses this technique.• High-Altitude Tunnels - These are designed to test the effects of shock waves again various aircraft shapes in near

vacuum. In 1952 the University of California constructed the first two high-altitude wind tunnels. One for testingobjects at 50 to 70 miles above earth and the second one for tests at 80 to 200 miles above earth.[13]

Wind tunnel 14

V/STOL tunnels

V/STOL tunnels require large cross section area, but only small velocities. Since power varies with the cube ofvelocity, the power required for the operation is also less. An example for a V/STOL tunnel is the NASA Langley14' X 22'tunnel.[14]

Spin tunnels

Aircraft have a tendency to go to spin when they stall (flight). These tunnels are used to study that phenomenon.

Automobile tunnelsAutomobile tunnels are of two categories:•• external flow tunnels - Used to study the external flow through the chassis•• climatic tunnels - Used to evaluate the performance of door systems, braking systems etc. under various climatic

conditions. Most of the leading automobile manufacturers have their own climatic wind tunnelsWunibald Kamm "built the first full-scale wind tunnel for motor vehicles."

Aeroacoustic tunnelsThese tunnels are used in the studies of noise generated by flow and its suppression.

Vertical wind tunnel T-105 at CentralAerohydrodynamic Institute, Moscow, built in

1941 for aircraft testing

Aquadynamic flume

The aerodynamic principles of the wind tunnel work equally onwatercraft, except the water is more viscous and so sets greater forceson the object being tested. A looping flume is typically used forunderwater aquadynamic testing. The interaction between 2 differenttypes of fluids means that pure windtunnel testing is only partlyrelevant. However, a similar sort of research is done in a towing tank

Low-speed oversize liquid testing

Air is not always the best test medium to study small-scaleaerodynamic principles, due to the speed of the air flow and airfoilmovement. A study of fruit fly wings designed to understand how thewings produce lift was performed using a large tank of mineral oil andwings 100 times larger than actual size, in order to slow down the wingbeats and make the vortices generated by the insect wings easier to seeand understand.

Fan testing

Wind tunnel tests are also performed to measuring the air movement ofthe fans at a specific pressure exactly. By determining the environmental circumstances during the measuring and byrevising the air-tightness afterwards, the standardization of the data is warranted. There are two possible ways ofmeasurement: a complete fan or an impeller on a hydraulic installation. Two measuring tubes enable measurementsof lower air currents (< 30.000 m³/h) as well as higher air currents (< 60.000 m³/h). The determination of the Q/hcurve of the fan is one of the main objectives. To determine this curve (and to define other parameters) air technical,mechanical as well as electro technical data are measured:

Air technical:

Wind tunnel 15

•• Static pressure difference (Pa)•• Amount of moved air (m³/h)•• Average air speed (m/s)•• Specific efficiency (W/1000m³/h)•• EfficiencyElectro technical:•• Tension (V)•• Current (A)•• Cos φ• Admitted power (W) fan / impeller•• Rotations per minute (RPM)The measurement can take place on the fan or in the application in which the fan is used.

Wind engineering testingIn Wind Engineering, wind tunnel tests are used to measure the velocity around, and forces or pressures uponstructures. Very tall buildings, buildings with unusual or complicated shapes (such as a tall building with a parabolicor a hyperbolic shape), cable suspension bridges or cable stayed bridges are analyzed in specialized atmosphericboundary layer wind tunnels. These feature a long upwind section to accurately represent the wind speed andturbulence profile acting on the structure. Wind tunnel tests provide the necessary design pressure measurements inuse of the dynamic analysis and control of tall buildings.

References[1] Going with the flow, Aerospace Engineering & Manufacturing, March 2009, pp. 27-28 Society of Automotive Engineers[2] Low-Reynolds-Number Airfoils, P.B.S. Lissaman, AeroVironment Inc., Pasadena, California, 91107 (http:/ / www. annualreviews. org/ doi/

pdf/ 10. 1146/ annurev. fl. 15. 010183. 001255)[3] "US Navy Experimental Wind Tunnel" (http:/ / books. google. com/ books?id=V3fmAAAAMAAJ& pg=PA426& dq=Aero+ Club+ Of+

America+ Flying& hl=en& ei=XbQqTeyqCdv4nwex5pHXAQ& sa=X& oi=book_result& ct=result& resnum=6&ved=0CEQQ6AEwBQ#v=onepage& q=Aero Club Of America Flying& f=true) Aerial Age Weekly, 17 January 1916, pages 426-427

[4] "Man Made Hurricane Tests Full Size Planes" Popular Mechanics, January 1936, pp.94-95 (http:/ / books. google. com/books?id=QdsDAAAAMBAJ& pg=PA94& dq=Popular+ Science+ 1935+ plane+ "Popular+ Mechanics"& hl=en&ei=QIs_TpjpHOPJsQKo4uC_Bw& sa=X& oi=book_result& ct=result& resnum=2& ved=0CCwQ6AEwATgU#v=onepage& q& f=true)

[5] "400mph Wind Tests Planes" (http:/ / books. google. com/ books?id=mtkDAAAAMBAJ& pg=PA14& dq=popular+ mechanics+ July+1932+ airplane& hl=en& ei=1EAYTerQFOe6nAfUv-TTDg& sa=X& oi=book_result& ct=result& resnum=6&ved=0CDgQ6AEwBTgy#v=onepage& q=popular mechanics July 1932 airplane& f=true) Popular Mechanics, July 1941

[6] Ernst Heinrich Hirschel, Horst Prem, Gero Madelung, Aeronautical Research in Germany: From Lilienthal Until Today Springer, 2004 ISBN354040645X, page 87

[7] "Wind at Work For Tomorrow's Planes." (http:/ / books. google. com/ books?id=TCEDAAAAMBAJ& pg=PA66& dq=popular+ science+1930& hl=en& ei=UY3MTsHTAsyltwfyz5xa& sa=X& oi=book_result& ct=result& resnum=4& ved=0CD4Q6AEwAzhG#v=onepage& q&f=true) Popular Science, July 1946, pp. 66-72.

[8] "Vertical Wind Tunnel." (http:/ / books. google. com/ books?id=AyEDAAAAMBAJ& pg=PA73& dq=popular+ science+ 1930& hl=en&ei=4dTRTu6lLsvUgAed8uifDQ& sa=X& oi=book_result& ct=result& resnum=5& ved=0CEIQ6AEwBDhG#v=onepage& q& f=true)Popular Science, February 1945, p. 73.

[9] http:/ / www. arnold. af. mil/ shared/ media/ document/ AFD-120305-099. pdf DAVID M. HIEBERT, PUBLIC LAW 81-415: THE UNITARYWIND TUNNEL PLAN ACT OF 1949 AND THE AIR ENGINEERING DEVELOPMENT CENTER ACT OF 19491, 2002 retrieved 2014 04 03

[10] Goldstein, E., "Wind Tunnels, Don't Count Them Out," Aerospace America, Vol. 48 #4, April 2010, pp. 38-43[11] Benjamin Gal-Or, "Vectored Propulsion, Supermaneuverability & Robot Aircraft", Springer Verlag, 1990, ISBN 0-387-97161-0, ISBN

3-540-97161-0[12] http:/ / vimeo. com/ 24212774[13] "Windless Wind Tunnels for High Altitude Tests." (http:/ / books. google. com/ books?id=8dwDAAAAMBAJ& pg=PA105& dq=1954+

Popular+ Mechanics+ January& hl=en& sa=X& ei=lYK0T7T1Es2dgQe5iMgH& ved=0CDoQ6AEwAjgy#v=onepage& q& f=true) PopularMechanics, February 1952, p. 105.

Wind tunnel 16

[14] 14'x22' Subsonic Wind Tunnel (http:/ / www. aeronautics. nasa. gov/ atp/ facilities/ 14x22/ index. html). Aeronautics.nasa.gov (2008-04-18).Retrieved on 2014-06-16.

•• Jewel B Barlow, William H Rae,Jr, Allan Pope: "Low speed wind tunnels testing" third edition ISBN9788126525683

Wind turbineThis article is about wind-powered electrical generators. For wind-powered machinery used to grind grain or pumpwater, see Windmill and Windpump.

Offshore wind farm, using 5 MW turbinesREpower 5M in the North Sea off the coast of

Belgium.

Renewableenergy

•• Biofuel•• Biomass•• Geothermal•• Hydropower•• Solar energy•• Tidal power•• Wave power•• Wind power•• Topics by country

•• v•• t• e [1]

A wind turbine is a device that converts kinetic energy from the wind into electrical power. A wind turbine used forcharging batteries may be referred to as a wind charger.

Wind turbine 17

The result of over a millennium of windmill development and modern engineering, today's wind turbines aremanufactured in a wide range of vertical and horizontal axis types. The smallest turbines are used for applicationssuch as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Slightly largerturbines can be used for making small contributions to a domestic power supply while selling unused power back tothe utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, are becoming anincreasingly important source of renewable energy and are used by many countries as part of a strategy to reducetheir reliance on fossil fuels.

HistoryMain article: History of wind power

James Blyth's electricity-generating wind turbine,photographed in 1891

The first megawatt-capacity wind turbine in theUSA, in 1941 Vermont

Windmills were used in Persia (present-day Iran) as early as 200 B.C.The windwheel of Heron of Alexandria marks one of the first knowninstances of wind powering a machine in history.[2][3] However, thefirst known practical windmills were built in Sistan, an Easternprovince of Iran, from the 7th century. These "Panemone" werevertical axle windmills, which had long vertical driveshafts withrectangular blades.[4] Made of six to twelve sails covered in reedmatting or cloth material, these windmills were used to grind grain ordraw up water, and were used in the gristmilling and sugarcaneindustries.[5]

Windmills first appeared in Europe during the middle ages. The firsthistorical records of their use in England date to the 11th or 12thcenturies and there are reports of German crusaders taking theirwindmill-making skills to Syria around 1190. By the 14th century,Dutch windmills were in use to drain areas of the Rhine delta.

The first electricity-generating wind turbine was a battery chargingmachine installed in July 1887 by Scottish academic James Blyth tolight his holiday home in Marykirk, Scotland. Some months laterAmerican inventor Charles F Brush built the first automaticallyoperated wind turbine for electricity production in Cleveland, Ohio.Although Blyth's turbine was considered uneconomical in the UnitedKingdom electricity generation by wind turbines was more costeffective in countries with widely scattered populations.

Wind turbine 18

The first automatically operated wind turbine,built in Cleveland in 1887 by Charles F. Brush. It

was 60 feet (18 m) tall, weighed 4 tons (3.6metric tonnes) and powered a 12 kW generator.

In Denmark by 1900, there were about 2500 windmills for mechanicalloads such as pumps and mills, producing an estimated combined peakpower of about 30 MW. The largest machines were on 24-meter (79 ft)towers with four-bladed 23-meter (75 ft) diameter rotors. By 1908there were 72 wind-driven electric generators operating in the US from5 kW to 25 kW. Around the time of World War I, American windmillmakers were producing 100,000 farm windmills each year, mostly forwater-pumping.[6] By the 1930s, wind generators for electricity werecommon on farms, mostly in the United States where distributionsystems had not yet been installed. In this period, high-tensile steel wascheap, and the generators were placed atop prefabricated open steellattice towers.

A forerunner of modern horizontal-axis wind generators was in serviceat Yalta, USSR in 1931. This was a 100 kW generator on a 30-meter(98 ft) tower, connected to the local 6.3 kV distribution system. It wasreported to have an annual capacity factor of 32 per cent, not muchdifferent from current wind machines.[7] In the autumn of 1941, the first megawatt-class wind turbine wassynchronized to a utility grid in Vermont. The Smith-Putnam wind turbine only ran for 1,100 hours before sufferinga critical failure. The unit was not repaired because of shortage of materials during the war.

The first utility grid-connected wind turbine to operate in the UK was built by John Brown & Company in 1951 inthe Orkney Islands.Despite these diverse developments, developments in fossil fuel systems almost entirely eliminated any wind turbinesystems larger than supermicro size. In the early 1970s, however, anti-nuclear protests in Denmark spurred artisanmechanics to develop microturbines of 22 kW. The organizing of owners into associations and co-operatives lead tothe lobbying of the government and utilities, which incentivized larger turbines throughout the 1980s and afterwards.Local activists in Germany, nascent turbine manufacturers in Spain, and large investors in the U.S. in the early 1990sthen lobbied for policies which stimulated the industry in those countries. Later companies formed in India andChina. As of 2012, Danish company Vestas is the world's biggest wind-turbine manufacturer.

Wind turbine 19

ResourcesMain article: Wind power

Nordex N117/2400 in Germany, a modernlow-wind turbine.

Wind turbines at the Jepirachí Eolian Park in LaGuajira, Colombia.

A quantitative measure of the wind energy available at any location iscalled the Wind Power Density (WPD) It is a calculation of the meanannual power available per square meter of swept area of a turbine, andis tabulated for different heights above ground. Calculation of windpower density includes the effect of wind velocity and air density.Color-coded maps are prepared for a particular area described, forexample, as "Mean Annual Power Density at 50 Metres". In the UnitedStates, the results of the above calculation are included in an indexdeveloped by the National Renewable Energy Laboratory and referredto as "NREL CLASS". The larger the WPD calculation, the higher it israted by class. Classes range from Class 1 (200 watts per square meteror less at 50 m altitude) to Class 7 (800 to 2000 watts per square m).Commercial wind farms generally are sited in Class 3 or higher areas,although isolated points in an otherwise Class 1 area may be practicalto exploit.

Wind turbines are classified by the wind speed they are designed for,from class I to class IV, with A or B referring to the turbulence.[8]

Class Avg Wind Speed (m/s)Turbulence

Ia 10 18%

IB 10 16%

IIA 8.5 18%

IIB 8.5 16%

IIIA 7.5 18%

IIIB 7.5 16%

IVA 6 18%

IVB 6 16%

Wind turbine 20

EfficiencyNot all the energy of blowing wind can be harvested, since conservation of mass requires that as much mass of airexits the turbine as enters it. Betz' law gives the maximal achievable extraction of wind power by a wind turbine as59% of the total kinetic energy of the air flowing through the turbine.Further inefficiencies, such as rotor blade friction and drag, gearbox losses, generator and converter losses, reducethe power delivered by a wind turbine. Commercial utility-connected turbines deliver about 75% of the Betz limit ofpower extractable from the wind, at rated operating speed.Efficiency can decrease slightly over time due to wear. Analysis of 3128 wind turbines older than 10 years inDenmark showed that half of the turbines had no decrease, while the other half saw a production decrease of 1.2%per year.[9]

Types

The three primary types: VAWT Savonius,HAWT towered; VAWT Darrieus as they appear

in operation

Wind turbines can rotate about either a horizontal or a vertical axis, theformer being both older and more common.

Horizontal axis

Components of a horizontal axis wind turbine(gearbox, rotor shaft and brake assembly) being

lifted into position

Horizontal-axis wind turbines (HAWT) have the main rotor shaft andelectrical generator at the top of a tower, and must be pointed into thewind. Small turbines are pointed by a simple wind vane, while largeturbines generally use a wind sensor coupled with a servo motor. Mosthave a gearbox, which turns the slow rotation of the blades into aquicker rotation that is more suitable to drive an electrical generator.

Since a tower produces turbulence behind it, the turbine is usuallypositioned upwind of its supporting tower. Turbine blades are madestiff to prevent the blades from being pushed into the tower by highwinds. Additionally, the blades are placed a considerable distance infront of the tower and are sometimes tilted forward into the wind asmall amount.

Downwind machines have been built, despite the problem of turbulence (mast wake), because they don't need anadditional mechanism for keeping them in line with the wind, and because in high winds the blades can be allowedto bend which reduces their swept area and thus their wind resistance. Since cyclical (that is repetitive) turbulencemay lead to fatigue failures, most HAWTs are of upwind design.

Wind turbine 21

A turbine blade convoy passing throughEdenfield, UK

Turbines used in wind farms for commercial production of electricpower are usually three-bladed and pointed into the wind bycomputer-controlled motors. These have high tip speeds of over320 km/h (200 mph), high efficiency, and low torque ripple, whichcontribute to good reliability. The blades are usually colored white fordaytime visibility by aircraft and range in length from 20 to 40 meters(66 to 131 ft) or more. The tubular steel towers range from 60 to 90meters (200 to 300 ft) tall. The blades rotate at 10 to 22 revolutions perminute. At 22 rotations per minute the tip speed exceeds 90 meters persecond (300 ft/s). A gear box is commonly used for stepping up thespeed of the generator, although designs may also use direct drive of anannular generator. Some models operate at constant speed, but moreenergy can be collected by variable-speed turbines which use a solid-state power converter to interface to thetransmission system. All turbines are equipped with protective features to avoid damage at high wind speeds, byfeathering the blades into the wind which ceases their rotation, supplemented by brakes.

Vertical axis design

A vertical axis Twisted Savoniustype turbine.

Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arrangedvertically. One advantage of this arrangement is that the turbine does not need tobe pointed into the wind to be effective, which is an advantage on a site wherethe wind direction is highly variable, for example when the turbine is integratedinto a building. Also, the generator and gearbox can be placed near the ground,using a direct drive from the rotor assembly to the ground-based gearbox,improving accessibility for maintenance.

The key disadvantages include the relatively low rotational speed with theconsequential higher torque and hence higher cost of the drive train, theinherently lower power coefficient, the 360 degree rotation of the aerofoil withinthe wind flow during each cycle and hence the highly dynamic loading on theblade, the pulsating torque generated by some rotor designs on the drive train,and the difficulty of modelling the wind flow accurately and hence the challengesof analysing and designing the rotor prior to fabricating a prototype.[10]

When a turbine is mounted on a rooftop the building generally redirects windover the roof and this can double the wind speed at the turbine. If the height of a rooftop mounted turbine tower isapproximately 50% of the building height it is near the optimum for maximum wind energy and minimum windturbulence. Wind speeds within the built environment are generally much lower than at exposed rural sites,[11] noisemay be a concern and an existing structure may not adequately resist the additional stress.

Subtypes of the vertical axis design include:Darrieus wind turbine

"Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus. Theyhave good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes topoor reliability. They also generally require some external power source, or an additional Savonius rotor tostart turning, because the starting torque is very low. The torque ripple is reduced by using three or moreblades which results in greater solidity of the rotor. Solidity is measured by blade area divided by the rotorarea. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connectedto the top bearing.[12]

Wind turbine 22

GiromillA subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety hasvariable pitch to reduce the torque pulsation and is self-starting. The advantages of variable pitch are: highstarting torque; a wide, relatively flat torque curve; a higher coefficient of performance; more efficientoperation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V,or curved blades may be used.

Savonius wind turbineThese are drag-type devices with two (or more) scoops that are used in anemometers, Flettner vents(commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They arealways self-starting if there are at least three scoops.

Twisted SavoniusTwisted Savonius is a modified savonius, with long helical scoops to provide smooth torque. This is often usedas a rooftop windturbine and has even been adapted for ships.[13]

Another type of vertical axis is the Parallel turbine, which is similar to the crossflow fan or centrifugal fan. It usesthe ground effect. Vertical axis turbines of this type have been tried for many years: a unit producing 10 kW wasbuilt by Israeli wind pioneer Bruce Brill in the 1980s.Wikipedia:Identifying reliable sources

Design and constructionMain article: Wind turbine design

Components of a horizontal-axis wind turbine

Inside view of a wind turbine tower, showing thetendon cables.

Wind turbines are designed to exploit the wind energy that exists at alocation. Aerodynamic modelling is used to determine the optimumtower height, control systems, number of blades and blade shape.

Wind turbines convert wind energy to electricity for distribution.Conventional horizontal axis turbines can be divided into threecomponents:•• The rotor component, which is approximately 20% of the wind

turbine cost, includes the blades for converting wind energy to lowspeed rotational energy.

• The generator component, which is approximately 34% of the windturbine cost, includes the electrical generator, the controlelectronics, and most likely a gearbox (e.g. planetary gearbox),adjustable-speed drive or continuously variable transmissioncomponent for converting the low speed incoming rotation to highspeed rotation suitable for generating electricity.

•• The structural support component, which is approximately 15% ofthe wind turbine cost, includes the tower and rotor yaw mechanism.

A 1.5 MW wind turbine of a type frequently seen in the United Stateshas a tower 80 meters (260 ft) high. The rotor assembly (blades andhub) weighs 22,000 kilograms (48,000 lb). The nacelle, which containsthe generator component, weighs 52,000 kilograms (115,000 lb). Theconcrete base for the tower is constructed using 26,000 kilograms(58,000 lb) of reinforcing steel and contains 190 cubic meters (250 cu yd) of concrete. The base is 15 meters (50 ft)in diameter and 2.4 meters (8 ft) thick near the center.

Wind turbine 23

Among all renewable energy systems wind turbines have the highest effective intensity of power-harvestingsurface[14] because turbine blades not only harvest wind power, but also concentrate it.[15]Wikipedia:Disputedstatement

Unconventional designsMain article: Unconventional wind turbines

The corkscrew shaped wind turbine atProgressive Field in Cleveland, Ohio

One E-66 wind turbine at Windpark Holtriem, Germany, carries anobservation deck, open for visitors. Another turbine of the same type,with an observation deck, is located in Swaffham, England. Airbornewind turbines have been investigated many times but have yet toproduce significant energy. Conceptually, wind turbines may also beused in conjunction with a large vertical solar updraft tower to extractthe energy due to air heated by the sun.

Wind turbines which utilise the Magnus effect have been developed.The ram air turbine is a specialist form of small turbine that is fitted tosome aircraft. When deployed, the RAT is spun by the airstream going past the aircraft and can provide power forthe most essential systems if there is a loss of all on–board electrical power.Wikipedia:Citation needed

Wind turbines on public displayMain article: Wind turbines on public display

The Nordex N50 wind turbine and visitor centreof Lamma Winds in Hong Kong, China

A few localities have exploited the attention-getting nature of windturbines by placing them on public display, either with visitor centersaround their bases, or with viewing areas farther away. The windturbines themselves are generally of conventional horizontal-axis,three-bladed design, and generate power to feed electrical grids, butthey also serve the unconventional roles of technology demonstration,public relations, and education.

Small wind turbines

Main article: Small wind turbine

Wind turbine 24

A small Quietrevolution QR5 Gorlovtype vertical axis wind turbine in

Bristol, England. Measuring 3 m indiameter and 5 m high, it has a

nameplate rating of 6.5 kW to thegrid.

Small wind turbines may be used for a variety of applications including on- oroff-grid residences, telecom towers, offshore platforms, rural schools and clinics,remote monitoring and other purposes that require energy where there is noelectric grid, or where the grid is unstable. Small wind turbines may be as smallas a fifty-watt generator for boat or caravan use. Hybrid solar and wind poweredunits are increasingly being used for traffic signage, particularly in rurallocations, as they avoid the need to lay long cables from the nearest mainsconnection point. The U.S. Department of Energy's National Renewable EnergyLaboratory (NREL) defines small wind turbines as those smaller than or equal to100 kilowatts.[16] Small units often have direct drive generators, direct currentoutput, aeroelastic blades, lifetime bearings and use a vane to point into the wind.

Larger, more costly turbines generally have geared power trains, alternatingcurrent output, flaps and are actively pointed into the wind. Direct drivegenerators and aeroelastic blades for large wind turbines are being researched.

Wind turbine spacing

On most horizontal windturbine farms, a spacing of about 6-10 times the rotor diameter is often upheld. However,for large wind farms distances of about 15 rotor diameters should be more economically optimal, taking into accounttypical wind turbine and land costs. This conclusion has been reached by research[17] conducted by CharlesMeneveau of the Johns Hopkins University, and Johan Meyers of Leuven University in Belgium, based on computersimulations that take into account the detailed interactions among wind turbines (wakes) as well as with the entireturbulent atmospheric boundary layer. Moreover, recent research by John Dabiri of Caltech suggests that verticalwind turbines may be placed much more closely together so long as an alternating pattern of rotation is createdallowing blades of neighbouring turbines to move in the same direction as they approach one another.[18]

Wind turbine braking systemWind Turbines disc pads [19] are formulated with ceramic compounds and brass chips instead of the commonly usedsemi-metallic pads steel fibers. The brass chips are able to transfer heat into the ceramic pad which acts like a heatsink then dissipates back into the rotor and atmosphere once the brakes have been released. Along with “Time–Released Lubricants” allowing the ceramic pads to handle higher brake temperatures with less heat fade, protectingthe calipers and pistons. A cooler running disc pad generates less wear on both pads rotors.

Wind turbine 25

Records

Fuhrländer Wind Turbine Laasow, inBrandenburg, Germany, among the

world's tallest wind turbines

Éole, the largest vertical axis windturbine, in Cap-Chat, Quebec,

Canada

Largest capacityThe Vestas V164 has a rated capacity of 8.0 MW,[20] has an overall heightof 220 m (722 ft), a diameter of 164 m (538 ft), and is the world'slargest-capacity wind turbine since its introduction in 2014. At least fivecompanies are working on the development of a 10 MW turbine.

Largest swept areaThe turbine with the largest swept area is the Samsung S7.0-171, with adiameter of 171 m, giving a total sweep of 22966 m2.

TallestVestas V164 is the tallest wind turbine, standing in Østerild, Denmark, 220meters tall, constructed in 2014.

Highest towerFuhrländer install a 2.5MW turbine on a 160m lattice tower in 2003 (seeFuhrländer Wind Turbine Laasow)

Largest vertical-axisLe Nordais wind farm in Cap-Chat, Quebec has a vertical axis windturbine (VAWT) named Éole, which is the world's largest at 110 m. It hasa nameplate capacity of 3.8 MW.

Largest 2 bladed turbineToday's biggest 2 bladed turbine is build by Mingyang Wind Power in2013. It is a SCD6.5MW offshore downwind turbine, designed by aerodynEnergiesysteme[21][22]

Most southerlyThe turbines currently operating closest to the South Pole are threeEnercon E-33 in Antarctica, powering New Zealand's Scott Base and theUnited States' McMurdo Station since December 2009 although a modifiedHR3 turbine from Northern Power Systems operated at theAmundsen-Scott South Pole Station in 1997 and 1998.[23] In March 2010CITEDEF designed, built and installed a wind turbine in ArgentineMarambio Base.[24]

Most productiveFour turbines at Rønland wind farm in Denmark share the record for the most productive wind turbines, witheach having generated 63.2 GWh by June 2010.

Highest-situatedSince 2013 the world's highest-situated wind turbine is made by United Windpower China GuodianCorporation installed by the Longyuan Power and located in the Naqu country, Tibet (China) around 4,800meters (15,700 ft) above sea level.[25][26] The site use a 1500 kW wind turbine designed by aerodynEnergiesysteme.[27]

Largest floating wind turbineThe world's largest—and also the first operational deep-water large-capacity—floating wind turbine is the 2.3 MW Hywind currently operating 10 kilometers (6.2 mi) offshore in 220-meter-deep water, southwest of

Wind turbine 26

Karmøy, Norway. The turbine began operating in September 2009 and utilizes a Siemens 2.3 MW turbine.

External links• Harvesting the Wind (45 lectures about wind turbines by professor Magdi Ragheb) [28]

• Wind Projects [29]

• Guided tour on wind energy [30]

• U.S. Wind Turbine Manufacturing: Federal Support for an Emerging Industry [31] Congressional ResearchService

• Wind Energy Technology World Wind Energy Association [32]

• Wind turbine simulation, National Geographic [33]

• Airborne Wind Industry Association international [34]

• The world's 10 biggest wind turbines [35]

• The Tethys database seeks to gather, organize and make available information on potential environmental effectsof offshore wind energy development [36]

Further reading• Tony Burton, David Sharpe, Nick Jenkins, Ervin Bossanyi: Wind Energy Handbook, John Wiley & Sons, 1st

edition (2001), ISBN 0-471-48997-2• Darrell, Dodge, Early History Through 1875 [37], TeloNet Web Development, Copyright 1996–2001• Robert Gasch, Jochen Twele (ed.), Wind power plants. Fundamentals, design, construction and operation,

Springer 2012 ISBN 978-3-642-22937-4.• Erich Hau, Wind turbines: fundamentals, technologies, application, economics Springer, 2013 ISBN

978-3-642-27150-2 (preview on Google Books)• Siegfried Heier, Grid integration of wind energy conversion systems Wiley 2006, ISBN 978-0-470-86899-7.• Peter Jamieson, Innovation in Wind Turbine Design. Wiley & Sons 2011, ISBN 978-0-470-69981-2• David Spera (ed,) Wind Turbine Technology: Fundamental Concepts in Wind Turbine Engineering, Second

Edition (2009), ASME Press, ISBN #: 9780791802601• Alois Schaffarczyk (ed.), Understanding wind power technology, Wiley & Sons 2014, ISBN 978-1-118-64751-6.• Hermann-Josef Wagner, Jyotirmay Mathur, Introduction to wind energy systems. Basics, technology and

operation. Springer 2013, ISBN 978-3-642-32975-3.• Ersen Erdem, Wind Turbine Industrial Applications [19]

References[1] http:/ / en. wikipedia. org/ w/ index. php?title=Template:Renewable_energy_sources& action=edit[2] A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145–151[3] Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp. 1–30 (10f.)[4] Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history, p. 54. Cambridge University Press. ISBN

0-521-42239-6.[5] Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald

Routledge Hill, Mechanical Engineering (http:/ / home. swipnet. se/ islam/ articles/ HistoryofSciences. htm))[6] Quirky old-style contraptions make water from wind on the mesas of West Texas (http:/ / www. mysanantonio. com/ news/ weather/

weatherwise/ stories/ MYSA092407. 01A. State_windmills. 3430a27. html)[7] Alan Wyatt: Electric Power: Challenges and Choices. Book Press Ltd., Toronto 1986, ISBN 0-920650-00-7[8] IEC Wind Turbine Classes (http:/ / www. wind-works. org/ articles/ IECWindTurbineClasses. html) June 7, 2006[9] Sanne Wittrup. " 11 years of wind data shows surprising production decrease (http:/ / ing. dk/ artikel/

11-aars-vinddata-afsloerede-overraskende-produktionsnedgang-163917)" (in Danish) Ingeniøren, 1 November 2013. Accessed: 2 November2013.

[10] http:/ / www. awsopenwind. org/ downloads/ documentation/ ModelingUncertaintyPublic. pdf[11] http:/ / www. urbanwind. net/ pdf/ technological_analysis. pdf

Wind turbine 27

[12][12] Exploit Nature-Renewable Energy Technologies by Gurmit Singh, Aditya Books, pp 378[13] Rob Varnon. Derecktor converting boat into hybrid passenger ferry (http:/ / www. ctpost. com/ news/ article/

Derecktor-converting-boat-into-hybrid-passenger-851170. php), Connecticut Post website, December 2, 2010. Retrieved April 25, 2012.[14] See Erich Hau: Windkraftanlagen: Grundlagen, Technik, Einsatz, Wirtschaftlichkeit. Berlin/ Heidelberg 2008, pp. 621. (German). (For the

english Edition see Erich Hau, Wind Turbines: Fundamentals, Technologies, Application, Economics, Springer 2005)[15][15] "Innovation in Wind Turbine Design" (2011), Peter Jamieson[16] Small Wind (http:/ / www. nrel. gov/ wind/ smallwind/ ), U.S. Department of Energy National Renewable Energy Laboratory website[17] J. Meyers and C. Meneveau, "Optimal turbine spacing in fully developed wind farm boundary layers" (2011), Wind Energy (http:/ /

onlinelibrary. wiley. com/ doi/ 10. 1002/ we. 469/ full)[18] Dabiri, J. Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays

(2011), J. Renewable Sustainable Energy 3, 043104 (http:/ / scitation. aip. org/ content/ aip/ journal/ jrse/ 3/ 4/ 10. 1063/ 1. 3608170)[19] http:/ / www. asadshop. com/ industrial. html[20] Wittrup, Sanne. " Power from Vestas' giant turbine (http:/ / ing. dk/ artikel/ saa-producerer-vestas-gigantmoelle-stroem-165903)" (in Danish.

English translation (http:/ / translate. google. com/ translate?hl=da& sl=da& tl=en& prev=_dd& u=http:/ / ing. dk/ artikel/saa-producerer-vestas-gigantmoelle-stroem-165903) ). Ingeniøren, 28 January 2014. Accessed: 28 January 2014.

[21] http:/ / www. windpoweroffshore. com/ article/ 1207686/ close---aerodyns-6mw-offshore-turbine-design[22] http:/ / www. windpowermonthly. com/ article/ 1188373/ ming-yang-install-65mw-offshore-turbine[23] Bill Spindler, The first Pole wind turbine (http:/ / www. southpolestation. com/ trivia/ 90s/ turbine. html).[24] GENERADOR DE ENERGÍA EÓLICA EN LA ANTÁRTIDA (http:/ / www. mindef. gov. ar/ info. asp?Id=1425)[25] http:/ / www. windpowermonthly. com/ article/ 1142093/ longyuan-builds-tibets-first-wind-farm[26] http:/ / www. renewable-energy-technology. net/ wind-energy-news/ china-firm-builds-world%E2%80%99s-highest-wind-farm-tibet[27] http:/ / www. eaton. com/ Eaton/ OurCompany/ SuccessStories/ Energy/ GuodianUnitedPowerTechnologyCompany/ index. htm[28] https:/ / netfiles. uiuc. edu/ mragheb/ www/ NPRE%20475%20Wind%20Power%20Systems/[29] http:/ / www. projectfreepower. com/[30] http:/ / www. windpower. org/ en/ knowledge/ guided_tour. html[31] https:/ / opencrs. com/ document/ R42023/[32] http:/ / www. wwindea. org/[33] http:/ / environment. nationalgeographic. com/ environment/ global-warming/ wind-power-interactive. html[34] http:/ / www. aweia. org/[35] http:/ / www. windpowermonthly. com/ 10-biggest-turbines/[36] http:/ / tethys. pnnl. gov/[37] http:/ / telosnet. com/ wind/ early. html

Engineering 28

EngineeringFor other uses, see Engineering (disambiguation).

The steam engine, a major driver in the Industrial Revolution, underscores the importanceof engineering in modern history. This beam engine is on display at the main building of

the ETSII (Superior Technical School of Industrial Engineering) of the TechnicalUniversity of Madrid, in Madrid, Spain.

Engineering (from Latin ingenium,meaning "cleverness" and ingeniare,meaning "to contrive, devise") is theapplication of scientific, economic,social, and practical knowledge inorder to invent, design, build, maintain,and improve structures, machines,devices, systems, materials andprocesses. The discipline ofengineering is extremely broad, andencompasses a range of morespecialized fields of engineering, eachwith a more specific emphasis onparticular areas of applied science,technology and types of application.

The American Engineers' Council forProfessional Development (ECPD, thepredecessor of ABET)[1] has defined"engineering" as:

The creative application of scientific principles to design or develop structures, machines, apparatus, ormanufacturing processes, or works utilizing them singly or in combination; or to construct or operate thesame with full cognizance of their design; or to forecast their behavior under specific operatingconditions; all as respects an intended function, economics of operation or safety to life andproperty.[2][3]

One who practices engineering is called an engineer, and those licensed to do so may have more formal designationssuch as Professional Engineer, Designated Engineering Representative, Chartered Engineer, Incorporated Engineer,Ingenieur or European Engineer.

HistoryMain article: History of engineeringEngineering has existed since ancient times as humans devised fundamental inventions such as the pulley, lever, andwheel. Each of these inventions is consistent with the modern definition of engineering, exploiting basic mechanicalprinciples to develop useful tools and objects.The term engineering itself has a much more recent etymology, deriving from the word engineer, which itself datesback to 1300, when an engine'er (literally, one who operates an engine) originally referred to "a constructor ofmilitary engines."[4] In this context, now obsolete, an "engine" referred to a military machine, i.e., a mechanicalcontraption used in war (for example, a catapult). Notable examples of the obsolete usage which have survived to thepresent day are military engineering corps, e.g., the U.S. Army Corps of Engineers.The word "engine" itself is of even older origin, ultimately deriving from the Latin ingenium (c. 1250), meaning"innate quality, especially mental power, hence a clever invention."[5]

Engineering 29

Later, as the design of civilian structures such as bridges and buildings matured as a technical discipline, the termcivil engineering entered the lexicon as a way to distinguish between those specializing in the construction of suchnon-military projects and those involved in the older discipline of military engineering.

Ancient era

The Ancient Romans built aqueducts to bring asteady supply of clean fresh water to cities and

towns in the empire.

The Pharos of Alexandria, the pyramids in Egypt, the HangingGardens of Babylon, the Acropolis and the Parthenon in Greece, theRoman aqueducts, Via Appia and the Colosseum, Teotihuacán and thecities and pyramids of the Mayan, Inca and Aztec Empires, the GreatWall of China, the Brihadeeswarar Temple of Thanjavur and tombs ofIndia, among many others, stand as a testament to the ingenuity andskill of the ancient civil and military engineers.

The earliest civil engineer known by name is Imhotep. As one of theofficials of the Pharaoh, Djosèr, he probably designed and supervisedthe construction of the Pyramid of Djoser (the Step Pyramid) atSaqqara in Egypt around 2630-2611 BC.[6]

Ancient Greece developed machines in both the civilian and militarydomains. The Antikythera mechanism, the first known mechanical computer,[7][8] and the mechanical inventions ofArchimedes are examples of early mechanical engineering. Some of Archimedes' inventions as well as theAntikythera mechanism required sophisticated knowledge of differential gearing or epicyclic gearing, two keyprinciples in machine theory that helped design the gear trains of the Industrial Revolution, and are still widely usedtoday in diverse fields such as robotics and automotive engineering.

Chinese, Greek and Roman armies employed complex military machines and inventions such as artillery which wasdeveloped by the Greeks around the 4th century B.C.,[9] the trireme, the ballista and the catapult. In the Middle Ages,the trebuchet was developed.

Renaissance eraThe first electrical engineer is considered to be William Gilbert, with his 1600 publication of De Magnete, whocoined the term "electricity".[10]

The first steam engine was built in 1698 by mechanical engineer Thomas Savery. The development of this devicegave rise to the Industrial Revolution in the coming decades, allowing for the beginnings of mass production.With the rise of engineering as a profession in the 18th century, the term became more narrowly applied to fields inwhich mathematics and science were applied to these ends. Similarly, in addition to military and civil engineeringthe fields then known as the mechanic arts became incorporated into engineering.

Engineering 30

Modern era

The International Space Station represents a modernengineering challenge from many disciplines.

Boeing 747-8 wing-fuselage sections during final assembly

The early stages of electrical engineering includedthe experiments of Alessandro Volta in the 1800s,the experiments of Michael Faraday, Georg Ohm andothers and the invention of the electric motor in1872. The work of James Maxwell and HeinrichHertz in the late 19th century gave rise to the field ofelectronics. The later inventions of the vacuum tubeand the transistor further accelerated the developmentof electronics to such an extent that electrical andelectronics engineers currently outnumber theircolleagues of any other engineering specialty.

The inventions of Thomas Savery and the Scottishengineer James Watt gave rise to modern mechanicalengineering. The development of specializedmachines and their maintenance tools during theindustrial revolution led to the rapid growth ofmechanical engineering both in its birthplace Britainand abroad.

John Smeaton was the first self-proclaimed civilengineer, and often regarded as the "father" of civilengineering. He was an English civil engineerresponsible for the design of bridges, canals,harbours and lighthouses. He was also a capablemechanical engineer and an eminent physicist.Smeaton designed the third Eddystone Lighthouse (1755–59) where he pioneered the use of 'hydraulic lime' (a formof mortar which will set under water) and developed a technique involving dovetailed blocks of granite in thebuilding of the lighthouse. His lighthouse remained in use until 1877 and was dismantled and partially rebuilt atPlymouth Hoe where it is known as Smeaton's Tower. He is important in the history, rediscovery of, anddevelopment of modern cement, because he identified the compositional requirements needed to obtain"hydraulicity" in lime; work which led ultimately to the invention of Portland cement.

Chemical engineering, like its counterpart mechanical engineering, developed in the nineteenth century during theIndustrial Revolution. Industrial scale manufacturing demanded new materials and new processes and by 1880 theneed for large scale production of chemicals was such that a new industry was created, dedicated to the developmentand large scale manufacturing of chemicals in new industrial plants. The role of the chemical engineer was thedesign of these chemical plants and processes.Aeronautical engineering deals with aircraft design while aerospace engineering is a more modern term that expandsthe reach of the discipline by including spacecraft design. Its origins can be traced back to the aviation pioneersaround the start of the 20th century although the work of Sir George Cayley has recently been dated as being fromthe last decade of the 18th century. Early knowledge of aeronautical engineering was largely empirical with someconcepts and skills imported from other branches of engineering.The first PhD in engineering (technically, applied science and engineering) awarded in the United States went toJosiah Willard Gibbs at Yale University in 1863; it was also the second PhD awarded in science in the U.S.Only a decade after the successful flights by the Wright brothers, there was extensive development of aeronautical engineering through development of military aircraft that were used in World War I . Meanwhile, research to provide

Engineering 31

fundamental background science continued by combining theoretical physics with experiments.In 1990, with the rise of computer technology, the first search engine was built by computer engineer Alan Emtage.

Main branches of engineeringMain article: List of engineering branches

Hoover Dam

Engineering, is a broad discipline which is often brokendown into several sub-disciplines. These disciplinesconcern themselves with differing areas of engineeringwork. Although initially an engineer will usually betrained in a specific discipline, throughout an engineer'scareer the engineer may become multi-disciplined,having worked in several of the outlined areas.Engineering is often characterized as having four mainbranches:[11][12]

• Chemical engineering – The application of physics,chemistry, biology, and engineering principles inorder to carry out chemical processes on acommercial scale, such as petroleum refining,microfabrication, fermentation, and biomoleculeproduction.

• Civil engineering – The design and construction of public and private works, such as infrastructure (airports,roads, railways, water supply and treatment etc.), bridges, dams, and buildings.

• Electrical engineering – The design and study of various electrical and electronic systems, such as electricalcircuits, generators, motors, electromagnetic/electromechanical devices, electronic devices, electronic circuits,optical fibers, optoelectronic devices, computer systems, telecommunications, instrumentation, controls, andelectronics.

• Mechanical engineering – The design of physical or mechanical systems, such as power and energy systems,aerospace/aircraft products, weapon systems, transportation products, engines, compressors, powertrains,kinematic chains, vacuum technology, and vibration isolation equipment.

The design of a modern auditorium involvesmany branches of engineering, including

acoustics, architecture and civil engineering.

Beyond these four, sources vary on other main branches. Historically,naval engineering and mining engineering were major branches.Modern fields sometimes included as majorbranchesWikipedia:Citation needed include manufacturingengineering, acoustical engineering, corrosion engineering,Instrumentation and control, aerospace, automotive, computer,electronic, petroleum, systems, audio, software, architectural,agricultural, biosystems, biomedical,[13] geological, textile, industrial,materials,[14] and nuclear[15] engineering. These and other branches ofengineering are represented in the 36 institutions forming themembership of the UK Engineering Council.

New specialties sometimes combine with the traditional fields andform new branches - for example Earth Systems Engineering and Management involves a wide range of subjectareas including anthropology, engineering, environmental science, ethics and philosophy. A new or emerging area of

application will commonly be defined temporarily as a permutation or subset of existing disciplines; there is often gray area as to when a given sub-field becomes large and/or prominent enough to warrant classification as a new

Engineering 32

"branch." One key indicator of such emergence is when major universities start establishing departments andprograms in the new field.For each of these fields there exists considerable overlap, especially in the areas of the application of sciences totheir disciplines such as physics, chemistry and mathematics.

Methodology

Design of a turbine requires collaboration of engineers frommany fields, as the system involves mechanical,

electro-magnetic and chemical processes. The blades, rotorand stator as well as the steam cycle all need to be carefully

designed and optimized.

Engineers apply mathematics and sciences such as physics tofind suitable solutions to problems or to make improvementsto the status quo. More than ever, engineers are now requiredto have knowledge of relevant sciences for their designprojects. As a result, they may keep on learning new materialthroughout their career.If multiple options exist, engineers weigh different designchoices on their merits and choose the solution that bestmatches the requirements. The crucial and unique task of theengineer is to identify, understand, and interpret theconstraints on a design in order to produce a successfulresult. It is usually not enough to build a technicallysuccessful product; it must also meet further requirements.Constraints may include available resources, physical,imaginative or technical limitations, flexibility for futuremodifications and additions, and other factors, such asrequirements for cost, safety, marketability, productibility,and serviceability. By understanding the constraints,engineers derive specifications for the limits within which aviable object or system may be produced and operated.

Problem solving

Engineers use their knowledge of science, mathematics, logic, economics, and appropriate experience or tacitknowledge to find suitable solutions to a problem. Creating an appropriate mathematical model of a problem allowsthem to analyze it (sometimes definitively), and to test potential solutions.

Usually multiple reasonable solutions exist, so engineers must evaluate the different design choices on their meritsand choose the solution that best meets their requirements. Genrich Altshuller, after gathering statistics on a largenumber of patents, suggested that compromises are at the heart of "low-level" engineering designs, while at a higherlevel the best design is one which eliminates the core contradiction causing the problem.

Engineers typically attempt to predict how well their designs will perform to their specifications prior to full-scaleproduction. They use, among other things: prototypes, scale models, simulations, destructive tests, nondestructivetests, and stress tests. Testing ensures that products will perform as expected.Engineers take on the responsibility of producing designs that will perform as well as expected and will not causeunintended harm to the public at large. Engineers typically include a factor of safety in their designs to reduce therisk of unexpected failure. However, the greater the safety factor, the less efficient the design may be.The study of failed products is known as forensic engineering, and can help the product designer in evaluating his orher design in the light of real conditions. The discipline is of greatest value after disasters, such as bridge collapses,when careful analysis is needed to establish the cause or causes of the failure.

Engineering 33

Computer use

A computer simulation of high velocity air flow around aSpace Shuttle during re-entry. Solutions to the flow requiremodelling of the combined effects of fluid flow and the heat

equations.

As with all modern scientific and technological endeavors,computers and software play an increasingly important role.As well as the typical business application software there area number of computer aided applications (computer-aidedtechnologies) specifically for engineering. Computers can beused to generate models of fundamental physical processes,which can be solved using numerical methods.

One of the most widely used design tools in the profession iscomputer-aided design (CAD) software like AutodeskInventor, DSS SolidWorks, or Pro Engineer which enablesengineers to create 3D models, 2D drawings, and schematicsof their designs. CAD together with digital mockup (DMU)and CAE software such as finite element method analysis oranalytic element method allows engineers to create modelsof designs that can be analyzed without having to make

expensive and time-consuming physical prototypes.

These allow products and components to be checked for flaws; assess fit and assembly; study ergonomics; and toanalyze static and dynamic characteristics of systems such as stresses, temperatures, electromagnetic emissions,electrical currents and voltages, digital logic levels, fluid flows, and kinematics. Access and distribution of all thisinformation is generally organized with the use of product data management software.

There are also many tools to support specific engineering tasks such as computer-aided manufacturing (CAM)software to generate CNC machining instructions; manufacturing process management software for productionengineering; EDA for printed circuit board (PCB) and circuit schematics for electronic engineers; MRO applicationsfor maintenance management; and AEC software for civil engineering.In recent years the use of computer software to aid the development of goods has collectively come to be known asproduct lifecycle management (PLM).

Social contextEngineering as a subject ranges from large collaborations to small individual projects. Almost all engineeringprojects are beholden to some sort of financing agency: a company, a set of investors, or a government. The fewtypes of engineering that are minimally constrained by such issues are pro bono engineering and open-designengineering.By its very nature engineering has interconnections with society and human behavior. Every product or constructionused by modern society will have been influenced by engineering. Engineering is a very powerful tool to makechanges to environment, society and economies, and its application brings with it a great responsibility. Manyengineering societies have established codes of practice and codes of ethics to guide members and inform the publicat large.Engineering projects can be subject to controversy. Examples from different engineering disciplines include thedevelopment of nuclear weapons, the Three Gorges Dam, the design and use of sport utility vehicles and theextraction of oil. In response, some western engineering companies have enacted serious corporate and socialresponsibility policies.Engineering is a key driver of human development.[16] Sub-Saharan Africa in particular has a very small engineering capacity which results in many African nations being unable to develop crucial infrastructure without outside

Engineering 34

aid.Wikipedia:Citation needed The attainment of many of the Millennium Development Goals requires theachievement of sufficient engineering capacity to develop infrastructure and sustainable technologicaldevelopment.[17]

All overseas development and relief NGOs make considerable use of engineers to apply solutions in disaster anddevelopment scenarios. A number of charitable organizations aim to use engineering directly for the good ofmankind:•• Engineers Without Borders•• Engineers Against Poverty•• Registered Engineers for Disaster Relief•• Engineers for a Sustainable World•• Engineering for Change• Engineering Ministries International[18]

Engineering companies in many established economies are facing significant challenges ahead with regard to thenumber of skilled engineers being trained, compared with the number retiring. This problem is very prominent in theUK.[19] There are many economic and political issues that this can cause, as well as ethical issues[20] It is widelyagreed that engineering faces an "image crisis",[21] rather than it being fundamentally an unattractive career. Muchwork is needed to avoid huge problems in the UK and well as the USA and other western economies.

Relationships with other disciplines

ScienceScientists study the world as it is; engineers create the world that has never been.

—Theodore von Kármán

Christopher Cassidy of NASA works on the Capillary FlowExperiment aboard the International Space Station.

There exists an overlap between the sciences andengineering practice; in engineering, one applies science.Both areas of endeavor rely on accurate observation ofmaterials and phenomena. Both use mathematics andclassification criteria to analyze and communicateobservations.Wikipedia:Citation needed

Scientists may also have to complete engineering tasks,such as designing experimental apparatus or buildingprototypes. Conversely, in the process of developingtechnology engineers sometimes find themselves exploringnew phenomena, thus becoming, for the moment,scientists.Wikipedia:Citation needed

In the book What Engineers Know and How They Know It, Walter Vincenti asserts that engineering research has acharacter different from that of scientific research. First, it often deals with areas in which the basic physics and/orchemistry are well understood, but the problems themselves are too complex to solve in an exact manner.

Examples are the use of numerical approximations to the Navier–Stokes equations to describe aerodynamic flowover an aircraft, or the use of Miner's rule to calculate fatigue damage. Second, engineering research employs manysemi-empirical methods that are foreign to pure scientific research, one example being the method of parametervariation.Wikipedia:Citation neededAs stated by Fung et al. in the revision to the classic engineering text Foundations of Solid Mechanics:

Engineering 35

"Engineering is quite different from science. Scientists try to understand nature. Engineers try to makethings that do not exist in nature. Engineers stress invention. To embody an invention the engineer mustput his idea in concrete terms, and design something that people can use. That something can be adevice, a gadget, a material, a method, a computing program, an innovative experiment, a new solutionto a problem, or an improvement on what is existing. Since a design has to be concrete, it must have itsgeometry, dimensions, and characteristic numbers. Almost all engineers working on new designs findthat they do not have all the needed information. Most often, they are limited by insufficient scientificknowledge. Thus they study mathematics, physics, chemistry, biology and mechanics. Often they haveto add to the sciences relevant to their profession. Thus engineering sciences are born."

Although engineering solutions make use of scientific principles, engineers must also take into account safety,efficiency, economy, reliability and constructability or ease of fabrication, as well as legal considerations such aspatent infringement or liability in the case of failure of the solution.Wikipedia:Citation needed

Medicine and biology

Leonardo da Vinci, seen here in a self-portrait, has beendescribed as the epitome of the artist/engineer. He is alsoknown for his studies on human anatomy and physiology.

The study of the human body, albeit from different directionsand for different purposes, is an important common linkbetween medicine and some engineering disciplines.Medicine aims to sustain, enhance and even replacefunctions of the human body, if necessary, through the use oftechnology.

Modern medicine can replace several of the body's functionsthrough the use of artificial organs and can significantly alterthe function of the human body through artificial devicessuch as, for example, brain implants and pacemakers.[22][23]

The fields of bionics and medical bionics are dedicated to thestudy of synthetic implants pertaining to natural systems.

Conversely, some engineering disciplines view the humanbody as a biological machine worth studying, and arededicated to emulating many of its functions by replacingbiology with technology. This has led to fields such asartificial intelligence, neural networks, fuzzy logic, androbotics. There are also substantial interdisciplinaryinteractions between engineering and medicine.[24][25]

Both fields provide solutions to real world problems. Thisoften requires moving forward before phenomena arecompletely understood in a more rigorous scientific senseand therefore experimentation and empirical knowledge is anintegral part of both.

Medicine, in part, studies the function of the human body. The human body, as a biological machine, has manyfunctions that can be modeled using engineering methods.[26]

The heart for example functions much like a pump,[27] the skeleton is like a linked structure with levers,[28] the brainproduces electrical signals etc.[29] These similarities as well as the increasing importance and application ofengineering principles in medicine, led to the development of the field of biomedical engineering that uses conceptsdeveloped in both disciplines.

Engineering 36

Newly emerging branches of science, such as systems biology, are adapting analytical tools traditionally used forengineering, such as systems modeling and computational analysis, to the description of biological systems.

Art

A drawing for a booster engine for steam locomotives.Engineering is applied to design, with emphasis on

function and the utilization of mathematics andscience.

There are connections between engineering and art;[30] they aredirect in some fields, for example, architecture, landscapearchitecture and industrial design (even to the extent that thesedisciplines may sometimes be included in a university's Faculty ofEngineering); and indirect in others.[31][32][33]

The Art Institute of Chicago, for instance, held an exhibition aboutthe art of NASA's aerospace design.[34] Robert Maillart's bridgedesign is perceived by some to have been deliberately artistic.[35]

At the University of South Florida, an engineering professor,through a grant with the National Science Foundation, has developed a course that connects art and engineering.[36]

Among famous historical figures Leonardo da Vinci is a well-known Renaissance artist and engineer, and a primeexample of the nexus between art and engineering.[][37]

Other fieldsIn political science the term engineering has been borrowed for the study of the subjects of social engineering andpolitical engineering, which deal with forming political and social structures using engineering methodology coupledwith political science principles. Financial engineering has similarly borrowed the term.

References[1] ABET History (http:/ / www. abet. org/ History/ )[2] Engineers' Council for Professional Development. (1947). Canons of ethics for engineers (http:/ / www. worldcatlibraries. org/ oclc/

26393909& referer=brief_results)[3] Engineers' Council for Professional Development definition on Encyclopædia Britannica (http:/ / www. britannica. com/ eb/ article-9105842/

engineering) (Includes Britannica article on Engineering)[4][4] Oxford English Dictionary[5] Origin: 1250–1300; ME engin < AF, OF < L ingenium nature, innate quality, esp. mental power, hence a clever invention, equiv. to in- +

-genium, equiv. to gen- begetting; Source: Random House Unabridged Dictionary, Random House, Inc. 2006.[6] Barry J. Kemp, Ancient Egypt, Routledge 2005, p. 159[7] " The Antikythera Mechanism Research Project (http:/ / www. antikythera-mechanism. gr/ project/ general/ the-project. html)", The

Antikythera Mechanism Research Project. Retrieved 2007-07-01 Quote: "The Antikythera Mechanism is now understood to be dedicated toastronomical phenomena and operates as a complex mechanical "computer" which tracks the cycles of the Solar System."

[8] Wilford, John. (July 31, 2008). Discovering How Greeks Computed in 100 B.C. (http:/ / www. nytimes. com/ 2008/ 07/ 31/ science/31computer. html?hp). New York Times.

[9] Britannica on Greek civilization in the 5th century Military technology (http:/ / www. britannica. com/ EBchecked/ topic/ 244231/ancient-Greece/ 261062/ Military-technology) Quote: "The 7th century, by contrast, had witnessed rapid innovations, such as the introductionof the hoplite and the trireme, which still were the basic instruments of war in the 5th." and "But it was the development of artillery thatopened an epoch, and this invention did not predate the 4th century. It was first heard of in the context of Sicilian warfare against Carthage inthe time of Dionysius I of Syracuse."

[10] Merriam-Webster Collegiate Dictionary, 2000, CD-ROM, version 2.5.[11] Journal of the British Nuclear Energy Society: Volume 1 British Nuclear Energy Society - 1962 - Snippet view (http:/ / books. google. ca/

books?id=Hy9WAAAAMAAJ& q=In+ most+ universities+ it+ should+ be+ possible+ to+ cover+ the+ main+ branches+ of+ engineering,+ie+ civil,+ mechanical,+ electrical+ and+ chemical+ engineering+ in+ this+ way. & dq=In+ most+ universities+ it+ should+ be+ possible+ to+cover+ the+ main+ branches+ of+ engineering,+ ie+ civil,+ mechanical,+ electrical+ and+ chemical+ engineering+ in+ this+ way. & hl=en&ei=2UkYTff0MZL-ngfesbGMDg& sa=X& oi=book_result& ct=result& resnum=1& ved=0CCoQ6AEwAA) Quote: In most universities itshould be possible to cover the main branches of engineering, i.e. civil, mechanical, electrical and chemical engineering in this way. Morespecialised fields of engineering application, of which nuclear power is ...

Engineering 37

[12] The Engineering Profession (https:/ / web. archive. org/ web/ 20070810194330/ http:/ / www. engc. org. uk/ documents/ Hamilton. pdf) bySir James Hamilton, UK Engineering Council Quote: "The Civilingenior degree encompasses the main branches of engineering civil,mechanical, electrical, chemical." (From the Internet Archive)

[13][13] Bronzino JD, ed., The Biomedical Engineering Handbook, CRC Press, 2006, ISBN 0-8493-2121-2[14] http:/ / www. jstor. org/ pss/ 10. 1525/ hsps. 2001. 31. 2. 223[15] http:/ / www. careercornerstone. org/ pdf/ nuclear/ nuceng. pdf[16] PDF on Human Development (http:/ / www. ewb-uk. org/ system/ files?file=Hinton lecture text FINAL. pdf)[17] MDG info pdf (http:/ / www. sistech. co. uk/ media/ ICEBrunelLecture2006. pdf?Docu_id=1420& faculty=14)[18] Home page for EMI (http:/ / www. emiusa. org/ index. html)[19] http:/ / www. engineeringuk. com/ About_us/[20] http:/ / www. georgededwards. co. uk/ policy/ why-does-it-matter-why-are-engineering-skills-important[21] http:/ / www. georgededwards. co. uk/ the-era-foundation-report. html[22] Ethical Assessment of Implantable Brain Chips. Ellen M. McGee and G. Q. Maguire, Jr. from Boston University (http:/ / www. bu. edu/

wcp/ Papers/ Bioe/ BioeMcGe. htm)[23] IEEE technical paper: Foreign parts (electronic body implants).by Evans-Pughe, C. quote from summary: Feeling threatened by cyborgs?

(http:/ / ieeexplore. ieee. org/ Xplore/ login. jsp?url=/ iel5/ 2188/ 27125/ 01204814. pdf?arnumber=1204814)[24] Institute of Medicine and Engineering: Mission statement The mission of the Institute for Medicine and Engineering (IME) is to stimulate

fundamental research at the interface between biomedicine and engineering/physical/computational sciences leading to innovative applicationsin biomedical research and clinical practice. (http:/ / www. uphs. upenn. edu/ ime/ mission. html)

[25] IEEE Engineering in Medicine and Biology: Both general and technical articles on current technologies and methods used in biomedical andclinical engineering ... (http:/ / ieeexplore. ieee. org/ xpl/ RecentIssue. jsp?punumber=51)

[26] Royal Academy of Engineering and Academy of Medical Sciences: Systems Biology: a vision for engineering and medicine in pdf: quote1:Systems Biology is an emerging methodology that has yet to be defined quote2: It applies the concepts of systems engineering to the study ofcomplex biological systems through iteration between computational and/or mathematical modelling and experimentation. (http:/ / www.acmedsci. ac. uk/ images/ pressRelease/ 1170256174. pdf)

[27] Science Museum of Minnesota: Online Lesson 5a; The heart as a pump (http:/ / www. smm. org/ heart/ lessons/ lesson5a. htm)[28] Minnesota State University emuseum: Bones act as levers (http:/ / www. mnsu. edu/ emuseum/ biology/ humananatomy/ skeletal/

skeletalsystem. html)[29] UC Berkeley News: UC researchers create model of brain's electrical storm during a seizure (http:/ / www. berkeley. edu/ news/ media/

releases/ 2005/ 02/ 23_brainwaves. shtml)[30] Lehigh University project: We wanted to use this project to demonstrate the relationship between art and architecture and engineering (http:/

/ www3. lehigh. edu/ News/ news_story. asp?iNewsID=1781& strBack=/ campushome/ Default. asp)[31] National Science Foundation:The Art of Engineering: Professor uses the fine arts to broaden students' engineering perspectives (http:/ /

www. nsf. gov/ news/ news_summ. jsp?cntn_id=107990& org=NSF)[32] MIT World:The Art of Engineering: Inventor James Dyson on the Art of Engineering: quote: A member of the British Design Council,

James Dyson has been designing products since graduating from the Royal College of Art in 1970. (http:/ / mitworld. mit. edu/ video/ 362/ )[33] University of Texas at Dallas: The Institute for Interactive Arts and Engineering (http:/ / iiae. utdallas. edu/ )[34] Aerospace Design: The Art of Engineering from NASA's Aeronautical Research (http:/ / www. artic. edu/ aic/ exhibitions/ nasa/ overview.

html)[35] Princeton U: Robert Maillart's Bridges: The Art of Engineering: quote: no doubt that Maillart was fully conscious of the aesthetic

implications ... (http:/ / press. princeton. edu/ titles/ 137. html)[36] quote:..the tools of artists and the perspective of engineers.. (http:/ / www. chiefengineer. org/ content/ content_display. cfm/

seqnumber_content/ 2697. htm)[37] Drew U: user website: cites Bjerklie paper (http:/ / www. users. drew. edu/ ~ejustin/ leonardo. htm)

Further reading• Blockley, David (2012). Engineering: a very short introduction. New York: Oxford University Press.

ISBN 978-0-19-957869-6.• Dorf, Richard, ed. (2005). The Engineering Handbook (2 ed.). Boca Raton: CRC. ISBN 0-8493-1586-7.• Billington, David P. (1996-06-05). The Innovators: The Engineering Pioneers Who Made America Modern.

Wiley; New Ed edition. ISBN 0-471-14026-0.• Petroski, Henry (1992-03-31). To Engineer is Human: The Role of Failure in Successful Design. Vintage.

ISBN 0-679-73416-3.• Petroski, Henry (1994-02-01). The Evolution of Useful Things: How Everyday Artifacts-From Forks and Pins to

Paper Clips and Zippers-Came to be as They are. Vintage. ISBN 0-679-74039-2.

Engineering 38

• Lord, Charles R. (2000-08-15). Guide to Information Sources in Engineering. Libraries Unlimited. doi:10.1336/1563086999 (http:/ / dx. doi. org/ 10. 1336/ 1563086999). ISBN 1-56308-699-9.

• Vincenti, Walter G. (1993-02-01). What Engineers Know and How They Know It: Analytical Studies fromAeronautical History. The Johns Hopkins University Press. ISBN 0-8018-4588-2.

• Hill, Donald R. (1973-12-31) [1206]. The Book of Knowledge of Ingenious Mechanical Devices: Kitáb fí ma'rifatal-hiyal al-handasiyya. Pakistan Hijara Council. ISBN 969-8016-25-2.

External links• National Society of Professional Engineers position statement on Licensure and Qualifications for Practice (http:/

/ www. nspe. org/ GovernmentRelations/ TakeAction/ PositionStatements/ ps_lic_qual_prac. html)• National Academy of Engineering (NAE) (http:/ / www. nae. edu/ )• American Society for Engineering Education (ASEE) (http:/ / www. asee. org/ )• The US Library of Congress Engineering in History bibliography (http:/ / www. loc. gov/ rr/ scitech/

SciRefGuides/ eng-history. html)• ICES: Institute for Complex Engineered Systems, Carnegie Mellon University, Pittsburgh, PA (http:/ / www. ices.

cmu. edu)• History of engineering bibliography (http:/ / www. tc. umn. edu/ ~tmisa/ biblios/ hist_engineering. html) at

University of Minnesota

Aerodynamics"Aerodynamic" redirects here. For other uses, see Aerodynamic (disambiguation).

A vortex is created by the passage of an aircraft wing, revealed by smoke.Vortices are one of the many phenomena associated with the study of

aerodynamics.

Aerodynamics, from Greek ἀήρ aer (air) +δυναμική (dynamics), is a branch of dynamicsconcerned with studying the motion of air,particularly when it interacts with a solidobject, such as an airplane wing.Aerodynamics is a sub-field of fluid dynamicsand gas dynamics, and many aspects ofaerodynamics theory are common to thesefields. The term aerodynamics is often usedsynonymously with gas dynamics, with thedifference being that "gas dynamics" applies tothe study of the motion of all gases, not limitedto air.

Formal aerodynamics study in the modernsense began in the eighteenth century, althoughobservations of fundamental concepts such asaerodynamic drag have been recorded muchearlier. Most of the early efforts inaerodynamics worked towards achieving heavier-than-air flight, which was first demonstrated by Wilbur and OrvilleWright in 1903. Since then, the use of aerodynamics through mathematical analysis, empirical approximations, windtunnel experimentation, and computer simulations has formed the scientific basis for ongoing developments inheavier-than-air flight and a number of other technologies. Recent work in aerodynamics has focused on issuesrelated to compressible flow, turbulence, and boundary layers, and has become increasingly computational in nature.

Aerodynamics 39

HistoryMain article: History of aerodynamicsModern aerodynamics only dates back to the seventeenth century, but aerodynamic forces have been harnessed byhumans for thousands of years in sailboats and windmills, and images and stories of flight appear throughoutrecorded history, such as the Ancient Greek legend of Icarus and Daedalus. Fundamental concepts of continuum,drag, and pressure gradients, appear in the work of Aristotle and Archimedes.In 1726, Sir Isaac Newton became the first person to develop a theory of air resistance, making him one of the firstaerodynamicists. Dutch-Swiss mathematician Daniel Bernoulli followed in 1738 with Hydrodynamica, in which hedescribed a fundamental relationship between pressure, density, and velocity for incompressible flow known todayas Bernoulli's principle, which provides one method for calculating aerodynamic lift. In 1757, Leonhard Eulerpublished the more general Euler equations, which could be applied to both compressible and incompressible flows.The Euler equations were extended to incorporate the effects of viscosity in the first half of the 1800s, resulting inthe Navier-Stokes equations. The Navier-Stokes equations are the most general governing equations of fluid flowand are difficult to solve.

A replica of the Wright brothers' wind tunnel ison display at the Virginia Air and Space Center.Wind tunnels were key in the development and

validation of the laws of aerodynamics.

In 1799, Sir George Cayley became the first person to identify the fouraerodynamic forces of flight (weight, lift, drag, and thrust), as well asthe relationships between them,[1] outlining the work towardsachieving heavier-than-air flight for the next century. In 1871, FrancisHerbert Wenham constructed the first wind tunnel, allowing precisemeasurements of aerodynamic forces. Drag theories were developed byJean le Rond d'Alembert, Gustav Kirchhoff, and Lord Rayleigh. In1889, Charles Renard, a French aeronautical engineer, became the firstperson to reasonably predict the power needed for sustained flight.Otto Lilienthal, the first person to become highly successful with gliderflights, was also the first to propose thin, curved airfoils that wouldproduce high lift and low drag. Building on these developments as wellas research carried out in their own wind tunnel, the Wright brothersflew the first powered aircraft on December 17, 1903.

During the time of the first flights, Frederick W. Lanchester, Martin Wilhelm Kutta, and Nikolai Zhukovskyindependently created theories that connected circulation of a fluid flow to lift. Kutta and Zhukovsky went on todevelop a two-dimensional wing theory. Expanding upon the work of Lanchester, Ludwig Prandtl is credited withdeveloping the mathematics behind thin-airfoil and lifting-line theories as well as work with boundary layers.

As aircraft speed increased, designers began to encounter challenges associated with air compressibility at speedsnear or greater than the speed of sound. The differences in air flows under these conditions led to problems in aircraftcontrol, increased drag due to shock waves, and structural dangers due to aeroelastic flutter. The ratio of the flowspeed to the speed of sound was named the Mach number after Ernst Mach, who was one of the first to investigatethe properties of supersonic flow. William John Macquorn Rankine and Pierre Henri Hugoniot independentlydeveloped the theory for flow properties before and after a shock wave, while Jakob Ackeret led the initial work oncalculating the lift and drag of supersonic airfoils. Theodore von Kármán and Hugh Latimer Dryden introduced theterm transonic to describe flow speeds around Mach 1 where drag increases rapidly. This rapid increase in drag ledaerodynamicists and aviators to disagree on whether supersonic flight was achievable. The sound barrier was brokenfor the first time in 1947 using the Bell X-1 aircraft.By the time the sound barrier was broken, much of the subsonic and low supersonic aerodynamics knowledge had matured. The Cold War fueled an ever evolving line of high performance aircraft. Computational fluid dynamics began as an effort to solve for flow properties around complex objects and has rapidly grown to the point where

Aerodynamics 40

entire aircraft can be designed using a computer, with wind-tunnel tests followed by flight tests to confirm thecomputer predictions. Knowledge of supersonic and hypersonic aerodynamics has also matured since the 1960s, andthe goals of aerodynamicists have shifted from understanding the behavior of fluid flow to understanding how toengineer a vehicle to interact appropriately with the fluid flow. Designing aircraft for supersonic and hypersonicconditions, as well as the desire to improve the aerodynamic efficiency of current aircraft and propulsion systems,continues to fuel new research in aerodynamics, while work continues to be done on important problems in basicaerodynamic theory related to flow turbulence and the existence and uniqueness of analytical solutions to theNavier-Stokes equations.

Fundamental concepts

Forces of flight on an airfoil

Understanding the motion of air around an object (often called a flowfield) enables the calculation of forces and moments acting on theobject. In many aerodynamics problems, the forces of interest are thefundamental forces of flight: lift, drag, thrust, and weight. Of these, liftand drag are aerodynamic forces, i.e. forces due to air flow over a solidbody. Calculation of these quantities is often founded upon theassumption that the flow field behaves as a continuum. Continuumflow fields are characterized by properties such as velocity, pressure,density and temperature, which may be functions of spatial position and time. These properties may be directly orindirectly measured in aerodynamics experiments, or calculated from equations for the conservation of mass,momentum, and energy in air flows. Density, velocity, and an additional property, viscosity, are used to classify flowfields.

Flow classificationFlow velocity is used to classify flows according to speed regime. Subsonic flows are flow fields in which airvelocity throughout the entire flow is below the local speed of sound. Transonic flows include both regions ofsubsonic flow and regions in which the flow speed is greater than the speed of sound. Supersonic flows are definedto be flows in which the flow speed is greater than the speed of sound everywhere. A fourth classification,hypersonic flow, refers to flows where the flow speed is much greater than the speed of sound. Aerodynamicistsdisagree on the precise definition of hypersonic flow.Compressibility refers to whether or not the flow in a problem can have a varying density. Subsonic flows are oftenassumed to be incompressible, i.e. the density is assumed to be constant. Transonic and supersonic flows arecompressible, and neglecting to account for the changes in density in these flow fields when performing calculationswill yield inaccurate results.Viscosity is associated with the frictional forces in a flow. In some flow fields, viscous effects are very small, andsolutions may neglect to account for viscous effects. These approximations are called inviscid flows. Flows forwhich viscosity is not neglected are called viscous flows. Finally, aerodynamic problems may also be classified bythe flow environment. External aerodynamics is the study of flow around solid objects of various shapes (e.g. aroundan airplane wing), while internal aerodynamics is the study of flow through passages in solid objects (e.g. through ajet engine).

Aerodynamics 41

Continuum assumptionUnlike liquids and solids, gases are composed of discrete molecules which occupy only a small fraction of thevolume filled by the gas. On a molecular level, flow fields are made up of many individual collisions between gasmolecules and between gas molecules and solid surfaces. In most aerodynamics applications, however, this discretemolecular nature of gases is ignored, and the flow field is assumed to behave as a continuum. This assumptionallows fluid properties such as density and velocity to be defined anywhere within the flow.Validity of the continuum assumption is dependent on the density of the gas and the application in question. For thecontinuum assumption to be valid, the mean free path length must be much smaller than the length scale of theapplication in question. For example, many aerodynamics applications deal with aircraft flying in atmosphericconditions, where the mean free path length is on the order of micrometers. In these cases, the length scale of theaircraft ranges from a few meters to a few tens of meters, which is much larger than the mean free path length. Forthese applications, the continuum assumption holds. The continuum assumption is less valid for extremelylow-density flows, such as those encountered by vehicles at very high altitudes (e.g. 300,000 ft/90 km) or satellites inLow Earth orbit. In these cases, statistical mechanics is a more valid method of solving the problem than continuousaerodynamics. The Knudsen number can be used to guide the choice between statistical mechanics and thecontinuous formulation of aerodynamics.

Conservation lawsAerodynamic problems are typically solved using fluid dynamics conservation laws as applied to a fluid continuum.Three conservation principles are used:1. Conservation of mass: In fluid dynamics, the mathematical formulation of this principle is known as the mass

continuity equation, which requires that mass is neither created nor destroyed within a flow of interest.2. Conservation of momentum: In fluid dynamics, the mathematical formulation of this principle can be considered

an application of Newton's Second Law. Momentum within a flow of interest is only created or destroyed due tothe work of external forces, which may include both surface forces, such as viscous (frictional) forces, and bodyforces, such as weight. The momentum conservation principle may be expressed as either a single vector equationor a set of three scalar equations, derived from the components of the three-dimensional velocity vector. In itsmost complete form, the momentum conservation equations are known as the Navier-Stokes equations. TheNavier-Stokes equations have no known analytical solution, and are solved in modern aerodynamics usingcomputational techniques. Because of the computational cost of solving these complex equations, simplifiedexpressions of momentum conservation may be appropriate to specific applications. The Euler equations are a setof momentum conservation equations which neglect viscous forces used widely by modern aerodynamicists incases where the effect of viscous forces is expected to be small. Additionally, Bernoulli's equation is a solution tothe momentum conservation equation of an inviscid flow, neglecting gravity.

3. Conservation of energy: The energy conservation equation states that energy is neither created nor destroyedwithin a flow, and that any addition or subtraction of energy is due either to the fluid flow in and out of the regionof interest, heat transfer, or work.

The ideal gas law or another equation of state is often used in conjunction with these equations to form a determinedsystem to solve for the unknown variables.

Aerodynamics 42

Branches of aerodynamicsAerodynamic problems are classified by the flow environment or properties of the flow, including flow speed,compressibility, and viscosity. External aerodynamics is the study of flow around solid objects of various shapes.Evaluating the lift and drag on an airplane or the shock waves that form in front of the nose of a rocket are examplesof external aerodynamics. Internal aerodynamics is the study of flow through passages in solid objects. For instance,internal aerodynamics encompasses the study of the airflow through a jet engine or through an air conditioning pipe.Aerodynamic problems can also be classified according to whether the flow speed is below, near or above the speedof sound. A problem is called subsonic if all the speeds in the problem are less than the speed of sound, transonic ifspeeds both below and above the speed of sound are present (normally when the characteristic speed isapproximately the speed of sound), supersonic when the characteristic flow speed is greater than the speed of sound,and hypersonic when the flow speed is much greater than the speed of sound. Aerodynamicists disagree over theprecise definition of hypersonic flow; a rough definition considers flows with Mach numbers above 5 to behypersonic.The influence of viscosity in the flow dictates a third classification. Some problems may encounter only very smallviscous effects on the solution, in which case viscosity can be considered to be negligible. The approximations tothese problems are called inviscid flows. Flows for which viscosity cannot be neglected are called viscous flows.

Incompressible aerodynamicsAn incompressible flow is a flow in which density is constant in both time and space. Although all real fluids arecompressible, a flow problem is often considered incompressible if the effect of the density changes in the problemon the outputs of interest is small. This is more likely to be true when the flow speeds are significantly lower than thespeed of sound. Effects of compressibility are more significant at speeds close to or above the speed of sound. TheMach number is used to evaluate whether the incompressibility can be assumed or the flow must be solved ascompressible.

Subsonic flow

Subsonic (or low-speed) aerodynamics studies fluid motion in flows which are much lower than the speed of soundeverywhere in the flow. There are several branches of subsonic flow but one special case arises when the flow isinviscid, incompressible and irrotational. This case is called potential flow and allows the differential equations usedto be a simplified version of the governing equations of fluid dynamics, thus making available to the aerodynamicista range of quick and easy solutions.In solving a subsonic problem, one decision to be made by the aerodynamicist is whether to incorporate the effectsof compressibility. Compressibility is a description of the amount of change of density in the problem. When theeffects of compressibility on the solution are small, the aerodynamicist may choose to assume that density isconstant. The problem is then an incompressible low-speed aerodynamics problem. When the density is allowed tovary, the problem is called a compressible problem. In air, compressibility effects are usually ignored when theMach number in the flow does not exceed 0.3 (about 335 feet (102m) per second or 228 miles (366 km) per hour at60 °F). Above 0.3, the problem should be solved by using compressible aerodynamics.

Aerodynamics 43

Compressible aerodynamicsMain article: Compressible flowAccording to the theory of aerodynamics, a flow is considered to be compressible if its change in density withrespect to pressure is non-zero along a streamline. This means that - unlike incompressible flow - changes in densitymust be considered. In general, this is the case where the Mach number in part or all of the flow exceeds 0.3. TheMach .3 value is rather arbitrary, but it is used because gas flows with a Mach number below that value demonstratechanges in density with respect to the change in pressure of less than 5%. Furthermore, that maximum 5% densitychange occurs at the stagnation point of an object immersed in the gas flow and the density changes around the restof the object will be significantly lower. Transonic, supersonic, and hypersonic flows are all compressible.

Transonic flow

Main article: TransonicThe term Transonic refers to a range of velocities just below and above the local speed of sound (generally taken asMach 0.8–1.2). It is defined as the range of speeds between the critical Mach number, when some parts of theairflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow issupersonic. Between these speeds, some of the airflow is supersonic, and some is not.

Supersonic flow

Main article: SupersonicSupersonic aerodynamic problems are those involving flow speeds greater than the speed of sound. Calculating thelift on the Concorde during cruise can be an example of a supersonic aerodynamic problem.Supersonic flow behaves very differently from subsonic flow. Fluids react to differences in pressure; pressurechanges are how a fluid is "told" to respond to its environment. Therefore, since sound is in fact an infinitesimalpressure difference propagating through a fluid, the speed of sound in that fluid can be considered the fastest speedthat "information" can travel in the flow. This difference most obviously manifests itself in the case of a fluidstriking an object. In front of that object, the fluid builds up a stagnation pressure as impact with the object brings themoving fluid to rest. In fluid traveling at subsonic speed, this pressure disturbance can propagate upstream, changingthe flow pattern ahead of the object and giving the impression that the fluid "knows" the object is there and isavoiding it. However, in a supersonic flow, the pressure disturbance cannot propagate upstream. Thus, when thefluid finally does strike the object, it is forced to change its properties -- temperature, density, pressure, and Machnumber—in an extremely violent and irreversible fashion called a shock wave. The presence of shock waves, alongwith the compressibility effects of high-velocity (see Reynolds number) fluids, is the central difference betweensupersonic and subsonic aerodynamics problems.

Hypersonic flow

Main article: HypersonicIn aerodynamics, hypersonic speeds are speeds that are highly supersonic. In the 1970s, the term generally came torefer to speeds of Mach 5 (5 times the speed of sound) and above. The hypersonic regime is a subset of thesupersonic regime. Hypersonic flow is characterized by high temperature flow behind a shock wave, viscousinteraction, and chemical dissociation of gas.

Aerodynamics 44

Associated terminology

Different types flow analysis around an airfoil:  Potential flow theory  Boundary layerBoundary

layer flow theory  TurbulenceTurbulent wakeanalysis

The incompressible and compressible flow regimes produce manyassociated phenomena, such as boundary layers and turbulence.

Boundary layers

Main article: Boundary layerThe concept of a boundary layer is important in many aerodynamicproblems. The viscosity and fluid friction in the air is approximated asbeing significant only in this thin layer. This principle makesaerodynamics much more tractable mathematically.

TurbulenceMain article: TurbulenceIn aerodynamics, turbulence is characterized by chaotic, stochastic property changes in the flow. This includes lowmomentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.Flow that is not turbulent is called laminar flow.

Aerodynamics in other fieldsFurther information: Automotive aerodynamicsAerodynamics is important in a number of applications other than aerospace engineering. It is a significant factor inany type of vehicle design, including automobiles. It is important in the prediction of forces and moments in sailing.It is used in the design of mechanical components such as hard drive heads. Structural engineers also useaerodynamics, and particularly aeroelasticity, to calculate wind loads in the design of large buildings and bridges.Urban aerodynamics seeks to help town planners and designers improve comfort in outdoor spaces, create urbanmicroclimates and reduce the effects of urban pollution. The field of environmental aerodynamics studies the waysatmospheric circulation and flight mechanics affect ecosystems. The aerodynamics of internal passages is importantin heating/ventilation, gas piping, and in automotive engines where detailed flow patterns strongly affect theperformance of the engine. People who do wind turbine design use aerodynamics. A few aerodynamic equations areused as part of numerical weather prediction.

References[1] Cayley, George. "On Aerial Navigation" Part 1 (http:/ / www. aeronautics. nasa. gov/ fap/ OnAerialNavigationPt1. pdf), Part 2 (http:/ / www.

aeronautics. nasa. gov/ fap/ OnAerialNavigationPt2. pdf), Part 3 (http:/ / www. aeronautics. nasa. gov/ fap/ OnAerialNavigationPt3. pdf)Nicholson's Journal of Natural Philosophy, 1809-1810. (Via NASA). Raw text (http:/ / invention. psychology. msstate. edu/ i/ Cayley/ Cayley.html). Retrieved: 30 May 2010.

Further readingGeneral aerodynamics

• Anderson, John D. (2007). Fundamentals of Aerodynamics (4th ed.). McGraw-Hill. ISBN 0-07-125408-0. OCLC 60589123 (http:/ / www. worldcat. org/ oclc/ 60589123).

• Bertin, J. J.; Smith, M. L. (2001). Aerodynamics for Engineers (4th ed.). Prentice Hall. ISBN 0-13-064633-4.OCLC  47297603 (http:/ / www. worldcat. org/ oclc/ 47297603).

Aerodynamics 45

• Smith, Hubert C. (1991). Illustrated Guide to Aerodynamics (2nd ed.). McGraw-Hill. ISBN 0-8306-3901-2.OCLC  24319048 (http:/ / www. worldcat. org/ oclc/ 24319048).

• Craig, Gale (2003). Introduction to Aerodynamics. Regenerative Press. ISBN 0-9646806-3-7. OCLC  53083897(http:/ / www. worldcat. org/ oclc/ 53083897).

Subsonic aerodynamics

• Katz, Joseph; Plotkin, Allen (2001). Low-Speed Aerodynamics (2nd ed.). Cambridge University Press.ISBN 0-521-66552-3. OCLC  43970751 45992085 (http:/ / www. worldcat. org/ oclc/ 43970751+ 45992085).

Transonic aerodynamics

• Moulden, Trevor H. (1990). Fundamentals of Transonic Flow. Krieger Publishing Company.ISBN 0-89464-441-6. OCLC  20594163 (http:/ / www. worldcat. org/ oclc/ 20594163).

• Cole, Julian D; Cook, L. Pamela (1986). Transonic Aerodynamics. North-Holland. ISBN 0-444-87958-7. OCLC 13094084 (http:/ / www. worldcat. org/ oclc/ 13094084).

Supersonic aerodynamics

• Ferri, Antonio (2005). Elements of Aerodynamics of Supersonic Flows (Phoenix ed.). Dover Publications.ISBN 0-486-44280-2. OCLC  58043501 (http:/ / www. worldcat. org/ oclc/ 58043501).

• Shapiro, Ascher H. (1953). The Dynamics and Thermodynamics of Compressible Fluid Flow, Volume 1. RonaldPress. ISBN 978-0-471-06691-0. OCLC  11404735 174280323 174455871 45374029 (http:/ / www. worldcat.org/ oclc/ 11404735+ 174280323+ 174455871+ 45374029).

• Anderson, John D. (2004). Modern Compressible Flow. McGraw-Hill. ISBN 0-07-124136-1. OCLC  71626491(http:/ / www. worldcat. org/ oclc/ 71626491).

• Liepmann, H. W.; Roshko, A. (2002). Elements of Gasdynamics. Dover Publications. ISBN 0-486-41963-0.OCLC  47838319 (http:/ / www. worldcat. org/ oclc/ 47838319).

• von Mises, Richard (2004). Mathematical Theory of Compressible Fluid Flow. Dover Publications.ISBN 0-486-43941-0. OCLC  56033096 (http:/ / www. worldcat. org/ oclc/ 56033096).

• Hodge, B. K.; Koenig K. (1995). Compressible Fluid Dynamics with Personal Computer Applications. PrenticeHall. ISBN 0-13-308552-X. OCLC  31662199 (http:/ / www. worldcat. org/ oclc/ 31662199). ISBN0-13-308552-X.

Hypersonic aerodynamics

• Anderson, John D. (2006). Hypersonic and High Temperature Gas Dynamics (2nd ed.). AIAA.ISBN 1-56347-780-7. OCLC  68262944 (http:/ / www. worldcat. org/ oclc/ 68262944).

• Hayes, Wallace D.; Probstein, Ronald F. (2004). Hypersonic Inviscid Flow. Dover Publications.ISBN 0-486-43281-5. OCLC  53021584 (http:/ / www. worldcat. org/ oclc/ 53021584).

History of aerodynamics

• Chanute, Octave (1997). Progress in Flying Machines. Dover Publications. ISBN 0-486-29981-3. OCLC 37782926 (http:/ / www. worldcat. org/ oclc/ 37782926).

• von Karman, Theodore (2004). Aerodynamics: Selected Topics in the Light of Their Historical Development.Dover Publications. ISBN 0-486-43485-0. OCLC  53900531 (http:/ / www. worldcat. org/ oclc/ 53900531).

• Anderson, John D. (1997). A History of Aerodynamics: And Its Impact on Flying Machines. CambridgeUniversity Press. ISBN 0-521-45435-2. OCLC  228667184 231729782 35646587 (http:/ / www. worldcat. org/oclc/ 228667184+ 231729782+ 35646587).

Aerodynamics related to engineering

Ground vehicles

• Katz, Joseph (1995). Race Car Aerodynamics: Designing for Speed. Bentley Publishers. ISBN 0-8376-0142-8.OCLC  181644146 32856137 (http:/ / www. worldcat. org/ oclc/ 181644146+ 32856137).

Aerodynamics 46

• Barnard, R. H. (2001). Road Vehicle Aerodynamic Design (2nd ed.). Mechaero Publishing. ISBN 0-9540734-0-1.OCLC  47868546 (http:/ / www. worldcat. org/ oclc/ 47868546).

Fixed-wing aircraft

• Ashley, Holt; Landahl, Marten (1985). Aerodynamics of Wings and Bodies (2nd ed.). Dover Publications.ISBN 0-486-64899-0. OCLC  12021729 (http:/ / www. worldcat. org/ oclc/ 12021729).

• Abbott, Ira H.; von Doenhoff, A. E. (1959). Theory of Wing Sections: Including a Summary of Airfoil Data.Dover Publications. ISBN 0-486-60586-8. OCLC  171142119 (http:/ / www. worldcat. org/ oclc/ 171142119).

• Clancy, L.J. (1975). Aerodynamics. Pitman Publishing Limited. ISBN 0-273-01120-0. OCLC  16420565 (http:/ /www. worldcat. org/ oclc/ 16420565).

Helicopters

• Leishman, J. Gordon (2006). Principles of Helicopter Aerodynamics (2nd ed.). Cambridge University Press.ISBN 0-521-85860-7. OCLC  224565656 61463625 (http:/ / www. worldcat. org/ oclc/ 224565656+ 61463625).

• Prouty, Raymond W. (2001). Helicopter Performance, Stability, and Control. Krieger Publishing Company Press.ISBN 1-57524-209-5. OCLC  212379050 77078136 (http:/ / www. worldcat. org/ oclc/ 212379050+ 77078136).

• Seddon, J.; Newman, Simon (2001). Basic Helicopter Aerodynamics: An Account of First Principles in the FluidMechanics and Flight Dynamics of the Single Rotor Helicopter. AIAA. ISBN 1-56347-510-3. OCLC  4762395060850095 (http:/ / www. worldcat. org/ oclc/ 47623950+ 60850095).

Missiles

• Nielson, Jack N. (1988). Missile Aerodynamics. AIAA. ISBN 0-9620629-0-1. OCLC  17981448 (http:/ / www.worldcat. org/ oclc/ 17981448).

Model aircraft

• Simons, Martin (1999). Model Aircraft Aerodynamics (4th ed.). Trans-Atlantic Publications, Inc.ISBN 1-85486-190-5. OCLC  43634314 51047735 (http:/ / www. worldcat. org/ oclc/ 43634314+ 51047735).

Related branches of aerodynamics

Aerothermodynamics

• Hirschel, Ernst H. (2004). Basics of Aerothermodynamics. Springer. ISBN 3-540-22132-8. OCLC  22838329656755343 59203553 (http:/ / www. worldcat. org/ oclc/ 228383296+ 56755343+ 59203553).

• Bertin, John J. (1993). Hypersonic Aerothermodynamics. AIAA. ISBN 1-56347-036-5. OCLC  28422796 (http:/ /www. worldcat. org/ oclc/ 28422796).

Aeroelasticity

• Bisplinghoff, Raymond L.; Ashley, Holt; Halfman, Robert L. (1996). Aeroelasticity. Dover Publications.ISBN 0-486-69189-6. OCLC  34284560 (http:/ / www. worldcat. org/ oclc/ 34284560).

• Fung, Y. C. (2002). An Introduction to the Theory of Aeroelasticity (Phoenix ed.). Dover Publications.ISBN 0-486-49505-1. OCLC  55087733 (http:/ / www. worldcat. org/ oclc/ 55087733).

Boundary layers

• Young, A. D. (1989). Boundary Layers. AIAA. ISBN 0-930403-57-6. OCLC  19981526 (http:/ / www. worldcat.org/ oclc/ 19981526).

• Rosenhead, L. (1988). Laminar Boundary Layers. Dover Publications. ISBN 0-486-65646-2. OCLC  1761909021227855 (http:/ / www. worldcat. org/ oclc/ 17619090+ 21227855).

Turbulence

• Tennekes, H.; Lumley, J. L. (1972). A First Course in Turbulence. The MIT Press. ISBN 0-262-20019-8. OCLC 281992 (http:/ / www. worldcat. org/ oclc/ 281992).

• Pope, Stephen B. (2000). Turbulent Flows. Cambridge University Press. ISBN 0-521-59886-9. OCLC  174790280 42296280 43540430 67711662 (http:/ / www. worldcat. org/ oclc/ 174790280+ 42296280+

Aerodynamics 47

43540430+ 67711662).

External links• NASA Beginner's Guide to Aerodynamics (http:/ / www. grc. nasa. gov/ WWW/ K-12/ airplane/ bga. html)• Smithsonian National Air and Space Museum's How Things Fly website (http:/ / howthingsfly. si. edu)• Aerodynamics for Students (http:/ / www. aerodynamics4students. com)• Aerodynamics for Pilots (http:/ / selair. selkirk. bc. ca/ Training/ Aerodynamics/ index. html)• Aerodynamics and Race Car Tuning (http:/ / www. 240edge. com/ performance/ tuning-aero. html)• Aerodynamic Related Projects (http:/ / www. aerodyndesign. com)• eFluids Bicycle Aerodynamics (http:/ / www. efluids. com/ efluids/ pages/ bicycle. htm)• Application of Aerodynamics in Formula One (F1) (http:/ / www. forumula1. net/ 2006/ f1/ features/

car-design-technology/ aerodynamics/ )• Aerodynamics in Car Racing (http:/ / www. nas. nasa. gov/ About/ Education/ Racecar/ )• Aerodynamics of Birds (http:/ / wings. avkids. com/ Book/ Animals/ intermediate/ birds-01. html)• Aerodynamics and dragonfly wings (http:/ / www. public. iastate. edu/ ~huhui/ paper/ 2007/ AIAA-2007-0483.

pdf)

Article Sources and Contributors 48

Article Sources and ContributorsWind engineering  Source: http://en.wikipedia.org/w/index.php?oldid=593364537  Contributors: AJBrand, Afil, Alymousaad, Basar, Blue Eyes 42, CFD wind, CambridgeBayWeather, Ckatz,Dancergraham, Ebikeguy, Evolauxia, Floquenbeam, Flyfast, Fmm81can, Johnfos, Kaldari, Kumar326, LilHelpa, Mark Arsten, Mild Bill Hiccup, Nialljc, Niceguyedc, Nk, OnePt618, Pierre cb,Portrino, Shustov, Some jerk on the Internet, Syrthiss, TenOfAllTrades, Tgeairn, Thegreatdr, Thomaswilson12, West.andrew.g, Woohookitty, 30 anonymous edits

Wind tunnel  Source: http://en.wikipedia.org/w/index.php?oldid=613128458  Contributors: 7&6=thirteen, A2Kafir, A3RO, Alansohn, Alexknight12, Alymousaad, An d810, Ancheta Wis,Andrewman327, BD2412, BatteryIncluded, BenFrantzDale, Bgwhite, BilCat, BobDrzyzgula, BokicaK, Brutaldeluxe, Bubba hotep, C2joec2, CambridgeBayWeather, Canterbury Tail, Canthusus,Charles Matthews, Chlewey, Chris the speller, Closedmouth, Cobberv, Cocle, Commander Keane, CommonsDelinker, Compfreak7, ComputerGeezer, Cosmic Latte, Cyfal, D, DARTH SIDIOUS2, DMahalko, David.Monniaux, Dawnsmessage, De bezige bij, Denmueller, Dgw, Dirrival, Dl2000, DonFB, Doncram, Dtom, Dziban303, Dzordzm, EMBaero, Econterms, EdH, Eddiehimself,Elipongo, Enisbayramoglu, Epbr123, Feťour, Flip, Flyingdreams, Fmm81can, Fongs, Frankenpuppy, Fyrael, Gene Hobbs, Georgepehli, Good Olfactory, Goodlysheep, Gphoto, GrahamN, Greencaterpillar, GregorB, Gunter, Hda3ku, Howcheng, IJA, IVAN3MAN, Ian01, Iridescent, J.delanoy, JRHorse, Jackehammond, Japanese Searobin, Jbk12385, Jcmaco, JeLuF, Jeff220, Jmabel,Jmundo, Koavf, Kpuck1, KudzuVine, Lellis.easc, Leszek Jańczuk, Liftarn, Lockan, Logawi, Mac, Mac Davis, Magioladitis, Manop, Marek69, Markos Strofyllas, Materialscientist, Mattbondy,Mbubel, Mdrejhon, MementoVivere, Mirwin, Mogism, Mr.Z-man, Mysid, Mythealias, Nbonneel, Niceguyedc, Nyttend, Occhipinti47, Oldmanbiker, Ortolan88, PZierhut, Palmpilot900, Pearle,Pengo, Peruvianllama, Philip Trueman, PierreAbbat, Pinethicket, Plenumchamber, Pooh, Praveen pillay, Prolog, Qutezuce, R'n'B, RaseaC, Raymondwinn, Rich Farmbrough, RivGuySC,Rjwilmsi, Saddhiyama, SamuelFreli, Saperaud, Sdcoonce, SeanMack, Settles1, Shanes, Sladen, SoCalDonF, Stan J Klimas, Stephenb, Sun Creator, Surfer43, Suruena, Swdwolf, Taichi, Tenisotl,Terrek, Thadius856, The ed17, Thomas Larsen, Toytoy, Twang, Typ932, UltimatesocCer, Uwoljw, Vanhorn, Vdjole, VectorVictor, Ventilationfans, Verbal, Vivaldi, Vojtamraz, Vrenator,Wolfc01, Wolfkeeper, Wtshymanski, Yuriybrisk, Zanhsieh, ZooFari, Zzuuzz, 294 anonymous edits

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Article Sources and Contributors 49

Engineering  Source: http://en.wikipedia.org/w/index.php?oldid=614492855  Contributors: 026fatih, 0x6D667061, 10braunsteinc, 12345roza1234, 128.163.239.xxx, 130.159.254.xxx, 16@r,1exec1, 1qazxswedc, 205.188.198.xxx, 208.186.187.xxx, 212.153.190.xxx, 24.50.165.xxx, 28421u2232nfenfcenc, 4engr, 64.80.202.xxx, 6birc, 7, A bit iffy, ABF, AVand, Aaidilamindar,Aavindraa, Abraham70, AbsolutDan, Ach8, Acs272, Adam Bishop, Adolf Hi+ler the second, Adtechweb, Ahoerstemeier, Aillema, Ajraddatz, Alansohn, Aldie, AlexPlante, Alexk33alt,Alexmason14, Alexthe5th, Allan McInnes, Alnatour 2000, Alpha 4615, Anaxial, Anbu121, Ancheta Wis, Andre Engels, AndrewHowse, Andrewpmk, AndriuZ, Andy Dingley, Angela, Anger22,Ankit Maity, AnnaFrance, Anonymous Dissident, Ant har05, Anterior1, Anthere, Anthonyhase, Anticent, Antiuser, Ap, Arbor to SJ, Arindam.2011, Art LaPella, Arunmails, Assassin15,Aster554, Astudent, Av99, Avb, Avery.mabojie, Awonsgay, Awotter, AzaToth, Aziz Alwayse Boss, BAxelrod, Bakabaka, Balapuba, Baljitisgay, Barek, Barneca, Barneyboo, Basar, Bbb2007,Bee0916, Beetstra, Bekus, BellBoy32, BenBreen2003, Bender235, BethNaught, Bevo, Bharu12, Bhawani Gautam, BigFatBuddha, BigHairRef, Biolawyer, Blake-, Blaserules, Blue520,Bluemask, Bmeguru, Bob, Bobg1756, Bobo192, Boda77, Boivie, Bongwarrior, Bookofjude, BookwormUK, Boulaur, Brandy Frisky, Brenont, Brian the Editor, Brion VIBBER, BrookesAkram,Brown480, BryXEng, Bsv109, Butko, C messier, CUSENZA Mario, Cadiomals, Caknuck, Caltas, CambridgeBayWeather, Can't sleep, clown will eat me, CanadianLinuxUser, Canderson7,Canthusus, Cantus, Capricorn42, Caracaskid, Careercornerstone, Catdude, Cbdorsett, Cburnett, Cemalardil, Cessator, Chaos, CharlesC, Chase Hughey, Cheese86549, Chenzw, Choldax, Chris thespeller, ChrisGualtieri, Chrispreece2007, Christopher Parham, Churchman6718, Cireshoe, Cjlim, Clementina, Clyde frogg, Colonies Chris, Cometstyles, Commander Keane, CommonsDelinker,Conifer, Conversion script, Coolcaesar, Corinne68, Corti, Corwin8, Courcelles, Cpmrodriguez, CrazyCanuck, Cronholm144, Cryptic C62, CryptoDerk, Crzer07, Cschutte, Csyberblue,Cybercobra, D.H, DJ Clayworth, DVD R W, DVdm, Dalton951565, Dancter, DanielCD, Darigan, Davandron, David.Monniaux, DavidLeighEllis, DavidLevinson, Dbl2010, Dedoch, Dekisugi,Delldot, Denisarona, Dennis Weijers, DerHexer, Deshanel X, Devin122, Dhollm, Dialectric, Diannaa, Diberri, Dicklyon, Diderot, Dieselman, Dilliondelafloure, Dina, Dmitri Lytov,DocWatson42, Docu, Dolphin51, Donaldm314, Donmu, Donner60, Dori, Dr. Bek, Dr.K., DragonFly31, Drdestiny77, Drunkenmonkey, EALacey, Echo95, Edgar181, EdwardH, Efcmagnew,Egfiasee, Egmontaz, El C, Ela112, Elcielo917, Elipongo, Emanuelperez, Encephalon, Engeduaust, Engineering fan, Engini86, Engology, Epbr123, Ephebi, Epicgenius, Er factory, Eranjenes2,Eric Desart, Esanchez7587, Everyking, Excirial, Eyesnore, FF2010, FOK SD OA, FactsAndFigures, Fahsja, Fama Clamosa, Famallament, Fanman72, Farkas János, Femto, Fieldday-sunday,Finn-Zoltan, Fintor, Floquenbeam, Fluffernutter, Footwarrior, Fplay, Fraggle81, Freeformer, Friginator, Frood, Fubar Obfusco, FudgeFury, Funandtrvl, Func, Future Perfect at Sunrise, GColwell, G. 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Aerodynamics  Source: http://en.wikipedia.org/w/index.php?oldid=613598989  Contributors: 124Nick, 21655, 2D, 62.253.64.xxx, Aakashamistry, Abqwildcat, Acdx, Acroterion, Adsta01,AeroPsico, Agendapedia, Al3209, Alansohn, Albedo, Ale jrb, Alexf, Alias Flood, Allagappan.gnu, Allahmuhammed, Amakuru, Amber is awesome, Anaraug, Andonic, Andy Dingley,AndyTheGrump, Ankit Maity, Anonymous Dissident, Anville, Anynobody, Ariadacapo, Arnero, Arpingstone, Art Carlson, Ashwin18, AtheWeatherman, Aude, AugPi, Avarame, BMF81,Bart133, Bartledan, Beetstra, BeteNoir, BilCat, Black Kite, Blaxthos, Blckavnger, Bleh999, Bluerasberry, BoKu, Bobo192, Bongwarrior, BoomerAB, Bowakowa, Brian the Editor,BrightStarSky, Brunton, Bsadowski1, Burnside65, CAD6DEE2E8DAD95A, CWii, Cain6119, CambridgeBayWeather, Camw, Can't sleep, clown will eat me, Cannolis, Canyouhearmenow,Capricorn42, Carson56437, Ceoil, ChaosNil, Charles Matthews, Chris 73, Chris the speller, ChrisGualtieri, Chrislk02, Citicat, Clarince63, Cmichael, Coffee and TV, Collins432, Cometstyles,Conversion script, Corpx, Corvus coronoides, Crowsnest, D, D.H, DARTH SIDIOUS 2, DMurphy, Daniel Mietchen, Darth Panda, Davehi1, David R. Ingham, DavidCary, Dawn Bard, DerHexer,Dhaluza, Dinosaur puppy, Dolphin51, Donner60, Dorftrottel, Douglass.auld, Doulos Christos, Drbreznjev, Durin, EMBaero, EdgeOfEpsilon, Edward321, Edwy, El C, Eleven even,Encyclopediarocketman, Epbr123, Epicgenius, Epipelagic, Eric-Wester, EricEnfermero, Ericd, Ericoides, Excirial, Fallthroughheat, FisherQueen, Flinkinshmorph, Flyer22, Fraggle81, Fremsley,Friday, Funnybunny, Fæ, G-W, GGGG777, GRAHAMUK, Geoffrey Wickham, Giftlite, Gilliam, Gimmetrow, GirasoleDE, Gonzonoir, Graham87, GrahamN, Greatestrowerever, GreenEco,Guccigopackgo, Gun Powder Ma, Gunter, GurraJG, Haemo, Hall Monitor, HamburgerRadio, Hashem sfarim, Headbomb, Hede2000, Hhhippo, Hipertek, Hjmerkel, Hmrox, Hohum, Hotlorp,Hurricane111, Hyacinth, Hydrogen Iodide, IdreamofJeanie, Immunize, Infrogmation, Introductory adverb clause, Inwind, Iridescent, Ixfd64, J.delanoy, J8079s, JForget, Jagged 85, JakeWartenberg, James086, JamesBWatson, Jan1nad, Java7837, Jerzy, Jfiling, Jhsounds, Jmcc150, John, JohnI, Johnska7, Jordanrrr, Jpkotta, Jrockley, Julesd, Jusdafax, JustUser, KVDP, Kazubon,Keilana, Kingpin13, Kungfuadam, L Kensington, LAX, LearnMore, LeaveSleaves, Leszek Jańczuk, Liftarn, Lights, Literacola, Lkent 009, Lotje, Luk, Luna Santin, M0r4d, MER-C, Macduffman,MadScot, Magnus Manske, Magus732, Mailer diablo, Mandarax, Maniadis, Marek69, Martin451, Master son, Materialscientist, Mathmo, Mattb112885, Matthew Desjardins, McSly, Mdh81235,Mechefan, Mentifisto, Michael Belisle, Michael Hardy, MichaelMaggs, Michaelas10, Mike1, MikeLynch, Minimac's Clone, Mirwin, Mitch21236, Mlouns, Mmeijeri, Moe Epsilon, Moink,Motorhead, Movcha, Mr swordfish, MrFish, Mrf8128, Mrs.S.Reeves, Mxn, Mythealias, Nasnema, Ncmvocalist, Nick Number, Nickkid5, Nikai, Nimbus227, Ninar Haneris, Nonforma, Nposs,Nsaa, Nuno Tavares, Oda Mari, Olivier, Onco p53, Onebravemonkey, Opelio, Orthografer, OverlordQ, Party, Penguinboy2, Perfect Proposal, Peteypaws, Philip Trueman, Phydend, Piali,Pinethicket, Pinkadelica, Pironman, Player00, Pmlineditor, Poeloq, Polly, Pondsearcher, Poony, Poop33333333, PrestonH, PseudoSudo, Psycho Kirby, Pumeleon, Pvazteixeira, Pyrrhus16, Qst,Quantpole, QuantumEngineer, Quintote, RA0808, Ramaksoud2000, Randywombat, Raven in Orbit, RayAYang, Raymondwinn, Rbeas, Reatlas, Red Slash, Remnar, RexNL, Rholton, Riana,Rigadoun, Rjwilmsi, Robert the Devil, Robomaeyhem, Roke, Rory096, RoyBoy, Rrburke, Ruleke, S, Salih, Salvo46, Saruman438, Sceptre, SchreiberBike, Scott14, Seangies, Seaphoto, Semperf,Shirik, Shtamy, Skarebo, Skizzik, Slysplace, Sm8900, Smalljim, SmilesALot, Snoyes, Soliloquial, Solipsist, Someguy1221, Sonett72, Srleffler, Ssd, Ssd175, Stanley Ipkiss, Stardust8212,Steelpillow, Stizz, Surfer43, Sus scrofa, Svdmolen, T-9000, TBloemink, TGCP, THF, Tawker, Tgeairn, Thane, Thatperson, The Rambling Man, The Thing That Should Not Be, The cattr, Thesock that should not be, TheKMan, TheNeutroniumAlchemist, Tide rolls, Titodutta, Titoxd, Tobby72, Tomasz Prochownik, Tommy2010, Trakesht, Trappist the monk, Treecko1230, Treisijs,Tresiden, Trevor MacInnis, Trusilver, Uhai, Updogdude44, Useight, User A1, Utcursch, Vanished user sfijw8jh4tjkefs, Vanka5, Venny85, VernoWhitney, Versus22, WPjcm, Walrus068, WaltonOne, Waltpohl, Warofdreams, Watterson6969, Weatherman1126, Why Not A Duck, Wiki13, Wikipelli, Wikitanvir, Will Beback, William Avery, Wimt, Wolfkeeper, WoodyWerm, Wywin,Xanchester, Xmnemonic, Yamamoto Ichiro, Yamum1999, Yekrats, Yomattyyo, Youngoat, ZX81, ZeroOne, Zocky, Zzuuzz, 1171 anonymous edits

Image Sources, Licenses and Contributors 50

Image Sources, Licenses and ContributorsFile:Windkanal.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Windkanal.jpg  License: GNU Free Documentation License  Contributors: JeLuFFile:Cessna 182 model-wingtip-vortex.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Cessna_182_model-wingtip-vortex.jpg  License: Creative Commons Attribution-ShareAlike3.0 Unported  Contributors: BenFrantzDaleFile:WB Wind Tunnel.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:WB_Wind_Tunnel.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Originaluploader was Axda0002 at en.wikipediaFile:Windtunnel2.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Windtunnel2.JPG  License: GNU Free Documentation License  Contributors: Abdullah Köroğlu, Flappiefh,Fongs, Liftarn, PeterWD, Ronaldino, WikigFile:Bundesarchiv Bild 102-17158, Deutsche Versuchsanstalt für Luftfahrt.jpg  Source:http://en.wikipedia.org/w/index.php?title=File:Bundesarchiv_Bild_102-17158,_Deutsche_Versuchsanstalt_für_Luftfahrt.jpg  License: Creative Commons Attribution-Sharealike 3.0 Germany Contributors: Arbitrarily0, El Grafo, Martin H., Mattes, PeterWDFile:Kirsten wind tunnel 05.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Kirsten_wind_tunnel_05.jpg  License: Creative Commons Attribution 2.5  Contributors: Joe MabelFile:Man examining fan of Langley Research Center 16 foot transonic wind tunnel.jpg  Source:http://en.wikipedia.org/w/index.php?title=File:Man_examining_fan_of_Langley_Research_Center_16_foot_transonic_wind_tunnel.jpg  License: Public Domain  Contributors: NASAFile:Kirsten wind tunnel 08A.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Kirsten_wind_tunnel_08A.jpg  License: Creative Commons Attribution 2.5  Contributors: Joe MabelFile:Lift curve.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Lift_curve.svg  License: Public Domain  Contributors: botag.File:GIF Flow visualization.gif  Source: http://en.wikipedia.org/w/index.php?title=File:GIF_Flow_visualization.gif  License: Creative Commons Attribution-Sharealike 3.0  Contributors:UWAL CrewFile:Wing with minitufts.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wing_with_minitufts.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: UWALCrewFile:Wing air flow pattern.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wing_air_flow_pattern.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: UWALCrewFile:Oil flow vis on straight wing.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Oil_flow_vis_on_straight_wing.jpg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: UWAL CrewFile:Fog visualization.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Fog_visualization.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: User:GeorgepehliFile:Vertical wind tunnel at TsAGI.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Vertical_wind_tunnel_at_TsAGI.jpg  License: Creative Commons Attribution-Sharealike 2.0 Contributors: Yuriy Lapitskiy (User:Yuriybrisk)File:Windmills D1-D4 (Thornton Bank).jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Windmills_D1-D4_(Thornton_Bank).jpg  License: unknown  Contributors: Andy Dingley,Benh, Berrucomons, Biopics, Foroa, HUB, Homonihilis, Jahobr, Jkadavoor, Lamiot, Lycaon, Sultan11, Teratornis, Thierry Caro, UpstateNYer, 1 anonymous editsFile:James Blyth's 1891 windmill.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:James_Blyth's_1891_windmill.jpg  License: Public Domain  Contributors: UnknownFile:Wind turbine 1941.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wind_turbine_1941.jpg  License: Public Domain  Contributors: US GOVFile:Wind turbine 1888 Charles Brush.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wind_turbine_1888_Charles_Brush.jpg  License: Public Domain  Contributors: AnRo0002,EurekaLott, Foroa, J JMesserly, Teratornis, 1 anonymous editsFile:N117, Hohenahr 7.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:N117,_Hohenahr_7.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors: User:AndolFile:Jepirachí.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Jepirachí.jpg  License: Creative Commons Attribution 3.0  Contributors: EPM Empresas públicas de medellin, entidaddel gobierno colombianoFile:HAWT and VAWTs in operation medium.gif  Source: http://en.wikipedia.org/w/index.php?title=File:HAWT_and_VAWTs_in_operation_medium.gif  License: Public Domain Contributors: SsgxnhFile:Scout moor gearbox, rotor shaft and brake assembly.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Scout_moor_gearbox,_rotor_shaft_and_brake_assembly.jpg  License:Creative Commons Attribution-Share Alike 2.0 Generic  Contributors: Paul AndersonFile:Turbine Blade Convoy Passing through Edenfield.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Turbine_Blade_Convoy_Passing_through_Edenfield.jpg  License: CreativeCommons Attribution-Share Alike 2.0 Generic  Contributors: Paul AndersonFile:Twisted Savonius wind turbine in operation@60rpm.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Twisted_Savonius_wind_turbine_in_operation@60rpm.gif  License:Public Domain  Contributors: SsgxnhFile:EERE illust large turbine.gif  Source: http://en.wikipedia.org/w/index.php?title=File:EERE_illust_large_turbine.gif  License: Public Domain  Contributors: Office of Energy Efficiency andRenewable EnergyFile:WKA spannglieder.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:WKA_spannglieder.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors:User:VanGoreFile:Progressive Field Wind Turbine.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Progressive_Field_Wind_Turbine.jpg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: User:Astros4477File:Lamma wind turbine.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Lamma_wind_turbine.jpg  License: GNU Free Documentation License  Contributors: PatrickmakFile:Quietrevolution Bristol 3513051949.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Quietrevolution_Bristol_3513051949.jpg  License: Creative Commons Attribution 2.0 Contributors: Anders Sandberg from Oxford, UKFile:Windkraftanlage Laasow.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Windkraftanlage_Laasow.jpg  License: Creative Commons Attribution-Sharealike 2.0  Contributors:SPBer at de.wikipediaFile:Quebecturbine.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Quebecturbine.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Spiritrock4u (talk)Original uploader was Spiritrock4u at en.wikipediaImage:Maquina vapor Watt ETSIIM.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Maquina_vapor_Watt_ETSIIM.jpg  License: GNU Free Documentation License  Contributors:Nicolás PérezFile:Pont du gard.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Pont_du_gard.jpg  License: GNU Free Documentation License  Contributors: Bernard bill5, ClemRutter, Cyr,Hazhk, 2 anonymous editsImage:International Space Station after undocking of STS-132.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:International_Space_Station_after_undocking_of_STS-132.jpg License: Public Domain  Contributors: NASA/Crew of STS-132File:Boeing 747-8 Test Planes in Assembly.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Boeing_747-8_Test_Planes_in_Assembly.jpg  License: Creative CommonsAttribution-Sharealike 2.0  Contributors: Jeff McNeill from Chiang Mai, ThailandFile:Hoover dam from air.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Hoover_dam_from_air.jpg  License: Public Domain  Contributors: snakefisch, editorFile:Symphony Hall Birmingham.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Symphony_Hall_Birmingham.jpg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: Acs272, 1 anonymous editsImage:Dampfturbine Montage01.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Dampfturbine_Montage01.jpg  License: GNU Free Documentation License  Contributors: SiemensPressebildImage:CFD Shuttle.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:CFD_Shuttle.jpg  License: Public Domain  Contributors: NASAFile:Expedition 36 flight engineer Chris Cassidy.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Expedition_36_flight_engineer_Chris_Cassidy.jpg  License: Public Domain Contributors: Huntster, Morio, Stas1995Image:Leonardo da Vinci - presumed self-portrait - WGA12798.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Leonardo_da_Vinci_-_presumed_self-portrait_-_WGA12798.jpg License: Public Domain  Contributors: Aavindraa, Amandajm, Coyau, LezFraniak, RP88, Santosga, TwoWings, Velos a 3 euros, 1 anonymous edits

Image Sources, Licenses and Contributors 51

Image:Booster-Layout.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Booster-Layout.jpg  License: Public Domain  Contributors: AGoon, Ikiwaner, Mikhail Ryazanov, Morven,Oxam Hartog, Steffen M., Topory, 1 anonymous editsImage:Airplane vortex edit.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Airplane_vortex_edit.jpg  License: Public Domain  Contributors: NASA Langley Research Center(NASA-LaRC), Edited by Fir0002Image:WB Wind Tunnel.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:WB_Wind_Tunnel.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Originaluploader was Axda0002 at en.wikipediaFile:aeroforces.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Aeroforces.svg  License: Public Domain  Contributors: Amada44File:Types of flow analysis in fluid mechanics.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Types_of_flow_analysis_in_fluid_mechanics.svg  License: Creative CommonsAttribution-Sharealike 3.0  Contributors: User:Ariadacapo

License 52

LicenseCreative Commons Attribution-Share Alike 3.0//creativecommons.org/licenses/by-sa/3.0/