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Introduction to Vehicle Aerodynamics

MEE 519 Vehicle Aerodynamics

Lecture 1

Dr. Y. Mukkamala

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Design Aspects of Vehicle Aerodynamics

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Design Components in Vehicle Aerodynamics

Structural Design

Aesthetics

Streamlined : Low Drag

Rigidity and Durability

Shape and Detail Optimization

Performance

Top Speed

Fuel Consumption

Maneuverability

Vehicle Elasticity

Emissions

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Flow Visualization

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Flow Visualization

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Streamlines

Spacing between streamlines indicates

local velocity.Closer streamlines indicate high

velocity; and hence low pressure.

Streamlines closely spaced on top, andsparse at the bottom lead to a positivelift.

Flow orientation relative to vehicle

direction is angle of attack.High angle of attack leads to high drag.

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High vehicle speeds (>100 kmph) lead touncontrollable lift and pitching moments,and hence high drag.

Flow Spoilers and negative wings canreduce lift albeit at increased drag.

Cross wind sensitivity : Directional

stability of a vehicle in side winds(function of normalized yaw momentcoefficient).

Side wind sensitivity reduced by re-locating the C.G of the vehicle towards itsfront.

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Cooling

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Engine CoolingAdequate air flow for engine

cooling.Increasing engine power higher airflow rates.

Lowered front ends (higher stability)Reduced air flow area.

Compact vehicle designs : Reduced

space for radiators.Safety aspects : Hard edge at frontend; wide bumpers hindered air

flow.

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Shape OptimizationLow Drag

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Development of Vehicle Aerodynamics

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Development of Vehicle Aerodynamics

Borrowed ideas from ship design,

and aircraft designs.Vehicle aerodynamics differs fromaircraft design in terms of

unsuitability of lift force.Working fluid for vehicles is air, whilethat for ships is water.

Boundary layer separations, andmultiple low pressure wakes exist forvehicles. B.L is mostly attached for

aircrafts.

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Flow Field Around a Vehicle

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Related Fields : Aerodynamics

E l ti f th V hi l

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Evolution of the Vehicle

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Concepts borrowed from ship, andaircraft aerodynamics failed.

Initial vehicles were very slow, andnot streamlined.

Lack of accurate data for drag, lift

and other force and performanceindicators hampered aerodynamicdesign.

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Borrowed Shapes

ll d

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Camille Jenatzy : First Recordvehicle; 1899.

Electrically driven.

Broke the barrier of 100 kmph (62mph); Later reached top speed of 105.9kmph.

Torpedo shaped streamlined body.

Exposed driver and outer wheelsdisturbed good flow properties

Alf R f C t Ri tti

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Alfa Romeo of Count RicottiBody like an air-ship; built in 1913.

L/d = 3.0; much fuller than theJenatzy vehicle.

Enclosed driver and wheels; betterair flow features.

Integrated wheel model developedby Bergmann in 1912.

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Boat Tail Model of Audi Alpensieger