Aerodynamics in cars

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Aerodynamics in cars

• Tushar Kiran
• Third year (Mechanical)

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Aerodynamics in Cars

• Aerodynamics is itself a part of fluid dynamics,
  which is the study of the properties of a solid
  object displace a fluid such as air.
• For the performance of a typical passenger car,
  aerodynamics is an important consideration in the
  achievement of maximum fuel economy, as well as
  in creating auto body styling that is visually
  appealing.

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Terms to Know- Aerodynamics

• Fluid
• Mass
• Aerodynamics
• Drag
• Lift
• Rear Suction
• Down Force
• Frontal Area

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Fluid

• Air-
• Is a type of fluid such as water that can be
  directed or displaced
• Has mass and is measured in terms of pressure
• Applies direct and frictional forces to objects
  in motion

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Principles

• One should be aware of four aerodynamic
  principles-
• Drag
• Lift/Down Force
• Drag Coefficient
• Frontal Area

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Drag

• Drag is a combination of two forces that will
  work against the acceleration of your car.
• Frontal Pressure occurs when tiny molecules of
  air hit the front of your car and is forced away
  to make room for other molecules to hit it.
• Rear Suction occurs when an empty pocket of air
  is created in the back of your car resulting in a
  vacuum cleaner effect that tries to pull your car
  backward.

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Air Flow Rear Suction
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Lift and Down Force

• Lift is similar to rear suction in that a thin
  empty pocket occurs as air passes over a flat
  surface causing the car to lift.
• Down Force is due to high pressure in curved
  surfaces that causes the car to be pushed down.

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Lift and Down Force
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Drag Coefficient

• Drag Coefficient is a way of expressing how
  slippery a car is.
• The drag coefficient (CD) is a measure of the
  vehicle's aerodynamic efficiency.

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Frontal Area

• Frontal Area is the total of all surfaces in the
  front of your vehicle which cause drag.
• Area Length x Width

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Aerodynamic drag

• Aerodynamic drag (?/2) CD A V2, where ? is
  air density, A is the projected frontal area of
  the body, and V is velocity.
• Even though aerodynamic drag is critically
  dependent on the velocity, it is only the product
  CD times A that the designer can control.

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Past of Aerodynamics
A frontal area, b wheelbase, CD drag
coefficient
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Partition of Drag in Modern Cars

• Rear View Mirrors 3 - 6
• Engine Cooling 5 - 9
• Underbody 14 - 20
• Wheels, Rims and Wheel Housings 30 35
• Vehicle Body(Shape and Sealing) 39 - 42

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Vehicle Body

• Ergonomics is more and more important in new cars
  and for instance the height of new models is
  growing. Thus the accessibility is improved.

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Wheels, Rims and Wheel Housings
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Underbody
2
3
1
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Engine Cooling
Mercedes-Benz 350 SL
Mercedes-Benz SL 500
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Rear View Mirror
A CFD (Computational Fluid Dynamics) program can
be very useful to optimize the shape of the rear
view mirror. The pressure distribution on the
side shows clearly how the rear view mirror
influences the air flow on the side of the car
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Conclusion

• This short report leads actually to one major
  idea which is that the body of a car only
  contributes to roughly half of the total drag.
• The major improvement for future vehicles can be
  reached by a smoother design of the underside.
• Another important issue for drag reduction,
  certainly later on, will the replacement of rear
  view mirrors with cameras for instance.
• New passenger seat configurations, like the
  driver seat in the front, two passenger seats in
  the middle and one at the rear, would make it
  possible to design more streamlined vehicles,
  paying attention to the fact that a suitable
  ergonomics remains.