Tushar Kiran Third year (Mechanical) Aerodynamics in cars Tushar Kiran Third year (Mechanical)

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.

Terms to Know- Aerodynamics Fluid Mass Aerodynamics Drag Lift Rear Suction Down Force Frontal Area

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;

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

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.

Air Flow Rear Suction

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.

Lift and Down Force

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.

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

Aerodynamic drag Aerodynamic drag = (ρ/2) CD * A * V2, where ρ 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.

Past of Aerodynamics A = frontal area, b = wheelbase, CD = drag coefficient

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%

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.

Wheels, Rims and Wheel Housings

Underbody 2 3 1

Engine Cooling Mercedes-Benz 350 SL Mercedes-Benz SL 500

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

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.