Drag Force Full Report

8/10/2019 Drag Force Full Report

1/29

1

DRAG FORCE

IN FLOW OVERA BODY


2/29

2

1.0 CONTENT

BIL CONTENT PAGE

1 TITLE 1

2 CONTENT 2

3 ABSTRACT 3

4 OBJECTIVE 4

5 INTRODUCTION 5-6

6 THEORY 7-8

7 APPARATUS 9-10

8 PROCEDURE 11

9 DATA TABULATION 12

10 RESULT ANALYSIS 13-20

11 DISCUSSION 21-24

12 CONCLUSION 25-28

13 REFERENCE 29


3/29

3

2.0 ABSTRACT

This experiment to study the drag coefficient over range of velocity in the

test section for hemispherical. The drag coefficient value is depending on the Reynolds

number that has to be calculated. By plotting the graph drag coefficient against velocity

represent the characteristic drag coefficient for hemisphere and by calculating the drag

force and the average value was compared with the theoretical value to get the percentage

error.


4/29

4

3.0 OBJECTIVE

The objectives of this experiment are:

2.1 To measure the drag coefficient over a range of velocities in the test section forhemispherical (open end facing flow and open end facing downstream).


5/29


6/29

6

Figure 2 - Flow over a Cylinder

For a solid object moving through a fluid, the drag is the component of thenetaerodynamic

orhydrodynamicforce acting in the direction of the movement. The component perpendicular to

this direction is consideredlift.Therefore drag acts to oppose the motion of the object, and in a

powered vehicle it is overcome by thrust. Drag is a force and is therefore avector quantity having

both a magnitude and a direction. Drag acts in a direction that is opposite to the motion of the

aircraft.

For this experiment, we will study on movement of a body through a fluid medium such air

or water will give rise to resultant force acting on the body due to the effect of the pressure and

shear stress acting on the surface of the body. The resultant force can be divided into horizontal and

vertical components which are termed drag and lift forces respectively. These forces are described

schematically in figure below.
http://en.wikipedia.org/wiki/Net_forcehttp://en.wikipedia.org/wiki/Aerodynamicshttp://en.wikipedia.org/wiki/Hydrodynamicshttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Lift_(force)http://www.grc.nasa.gov/WWW/K-12/airplane/vectors.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/vectors.htmlhttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Hydrodynamicshttp://en.wikipedia.org/wiki/Aerodynamicshttp://en.wikipedia.org/wiki/Net_force


7/29

7

5.0 THEORY

When a fluid flows around a stationary cylinder or when a cylinder moves through a

stationary fluid, the fluid exerts a force on the cylinder called drag force. The sources of this dragare: (a) friction between the fluid and the surface of the cylinder, and (b) a non-uniform pressure

distribution.

The cylinder in the fluid stream presents a certain area perpendicular to the direction of fluid

motion. This is called the platform area of the cylinder (length x width (diameter) the fluid moves

toward and is deflected around the cylinder, some of its momentum is transferred to the cylinder in

the form of pressure on the projected area facing the flow.

If the flow follows the contour of the cylinder, the pressure on the side facing the flow is

balanced by the pressure on the reverse side in which case the pressure drag is very small or zero.

(See Figure 1). This condition is described by potential theory where the fluid is ideal and is realized

in real fluids at very low Reynolds numbers. At high Reynolds numbers, the flow does not follow the

contour of the cylinder, i.e., the boundary layer grows more rapidly for an adverse pressure gradient

and if the pressure gradient is large enough, separation may occur, and turbulent eddies form in the

wake of the cylinder. In this case the pressure on the reverse side fails to recover (see Figure 2)

leading to an unbalanced pressure distribution and pressure drag. Ordinarily, it is not practical to

separate the viscous and pressure drag forces, and indeed, it is usually their sum in which we are

interested. Therefore, the usual practice is to characterize their combined effects with two

dimensionless parameters, the drag coefficient:

Cd =

And the Reynolds number,

Where FDis the drag force, V is the free stream velocity, APis the platform area, and D is the cord

length of the shape (cylinder).


8/29

8

Figure 3 - Ideal fluid flow around a cylinder Figure 4 - Real fluid flow around a cylinder

The drag coefficient may be determined experimentally in two ways. The most obvious method is to

measure the drag force (FD) and the velocity (V) directly and then calculate Cdfrom equation 1. The

second method to determine drag force is to use the Moody chart with drag coefficient versus

Reynolds number for known shapes. Using the Moody chart in combination with the strain

measured in the experiment, the drag force can be found. The fluid velocity can be calculated from

the pressure recorded on the DAQ and the use of Bernoulli's equation.


9/29

9

6.0 APPARATUS

Figure 1:Rod, Hollow Hemispherical (rear and front)

Figure 2: Wind Tunnel


10/29

10

Figure 3:Balance Arm


11/29

11

7.0 PROCEDURE

1. The diameter of the hemisphere was measured

2. The rod was fit into the balance arm.

3. The balance arm was put to a balance start.

4. The blower fan was switched on and the flow was set to the velocity of 8m/s.

5. The arm was once again balanced and the reading was taken.

6. The velocity was increased by 2m/s until 20m/s, the arm balanced and the reading is

again taken.7. The hemisphere body was fit into the balance arm with the open end facing the flow.

8. Step 3 until 6 was repeated.

9. The hemisphere body was fit into the balance arm with the end of the open end

facing the downstream.

10.Step 3 until 6 was repeated.


12/29


13/29

13

9.0 DATA ANALYSIS

SAMPLE CALCULATION

Reading at velocity (8 m/s)

1. Air density in lab

2. Reynolds number

1.23

V = 8

D = 0.065 m

= 1.849 x

= 34592.00


14/29

14

3.

Net Drag Force, FD

Net Drag Force, FD = Drag Force Rigid Rod Drag Force

= 0.19

0.01= 0.18 N

4. Projected area of hemisphere

A

5. Drag Coefficient, CD ( upstream)

A= 3.318

V = 8

1.23

FD = 0.18 N


15/29

15

6.

Drag Coefficient, CD (downstream)

7. Net Drag Coefficient, CD

Net Drag Coefficient, CD = Drag Coefficient, CD (upstream) Drag Coefficient, CD(downstream)

= 1.378 = 0.459

8. Percentage of error of CD for open end facing downstream

CD theory = 0.4 CD exp = 0.578 (average)

Percentage error, %


16/29

16

9.

Percentage of error of CD for open end facing upstream

CD theory = 1.2 CD exp = 1.457 (average)

Percentage error, %


17/29

17


18/29

18


19/29

19


20/29

20


21/29

21

10.0 DISCUSSION

Abdul Aziz Bin Bahari (2013630114)


22/29


23/29

23

Fareez Bin Mohamad Nasir (2013869104)


24/29

24

Mohd Asyraf Bin Abdullah (20132286666)


25/29

25

11.0 CONCLUSION

Abdul Aziz Bin Bahari (2013630114)


26/29

26

Abdul Rahman Bin Mohamed Affandi (2013245276)


27/29

27

Fareez Bin Mohamad Nasir (2013869104)


28/29

28

Mohd Asyraf Bin Abdullah (20132286666)


29/29

12.0 REFERENCE

REFERENCES

INTERNET

1. http://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.html

2. http://www.engineeringtoolbox.com/laminar-transitional-turbulent-flow-d_577.html

3. http://www.efunda.com/formulae/fluids/calc_reynolds.cfm

4. http://en.wikipedia.org/wiki/Density_of_air

5. http://www.engineeringtoolbox.com/liquids-densities-d_743.html
http://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.htmlhttp://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.htmlhttp://www.engineeringtoolbox.com/laminar-transitional-turbulent-flow-d_577.htmlhttp://www.engineeringtoolbox.com/laminar-transitional-turbulent-flow-d_577.htmlhttp://www.efunda.com/formulae/fluids/calc_reynolds.cfmhttp://www.efunda.com/formulae/fluids/calc_reynolds.cfmhttp://en.wikipedia.org/wiki/Density_of_airhttp://en.wikipedia.org/wiki/Density_of_airhttp://www.engineeringtoolbox.com/liquids-densities-d_743.htmlhttp://www.engineeringtoolbox.com/liquids-densities-d_743.htmlhttp://www.engineeringtoolbox.com/liquids-densities-d_743.htmlhttp://en.wikipedia.org/wiki/Density_of_airhttp://www.efunda.com/formulae/fluids/calc_reynolds.cfmhttp://www.engineeringtoolbox.com/laminar-transitional-turbulent-flow-d_577.htmlhttp://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.html

Documents

Drag Force Full Report