Automotive aerodynamics

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Automotive aerodynamics is the study of the aerodynamics of road vehicles. The main concerns of automotive aerodynamics are reducing drag, reducing wind noise, and preventing undesired lift forces at high speeds. For some classes of racing vehicles, it may also be important to produce desirable downwards aerodynamic forces to improve traction and thus cornering abilities.

An aerodynamic automotive will integrate the wheel and lights in its shape to have a small surface. It will be streamlined, for example it does not have sharp edges crossing the wind stream above the windshield and will feature a sort of tail called a fastback. It will have a flat and smooth floor to support the Venturi effect and produce desirable downwards aerodynamic forces. The air rams into the engine bay, is used (cooling, combustion, and for passengers), reaccelerated by a nozzle and then ejected under the floor.

Automotive aerodynamics differs from aircraft aerodynamics in several ways. First, the characteristic shape of a road vehicle is bluff , compared to an aircraft. Second, the vehicle operates very close to the ground, rather than in free air. Third, the operating speeds are lower. Fourth, the ground vehicle has fewer degrees of freedom than the aircraft, and its motion is less affected by aerodynamic forces.

Automotive aerodynamics is studied using both computer modelling and wind tunnel testing. For the most accurate results from a wind tunnel test, the tunnel is sometimes equipped with a rolling road. This is a movable floor for the working section, which moves at the same speed as the air flow. This prevents a boundary layer forming on the floor of the working section and affecting the results.

Total Aerodynamic drag = Cd multiplied by the frontal area. The width and height of curvy cars lead to gross overestimations of frontal area. These numbers use the manufacturer's frontal area specs from <http://www.mayfco.com/tbls.htm>

Some examples:

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