A new aerodynamic approach to advanced automobile basic shapes

Aerodynamic basic shapes are generally intended as non wheeled bodies moving at a small distance from the ground, effective and suitable for automobile applications. The shape is furthermore designed to comply with requirements other than aerodynamic accomodating occupants, luggage and mechanical parts within as small as possible overall dimensions. However, even though the basic body drag coefficient can be as low as 0.05, the addition of wheels may increase the body drag, by two to three times. The new approach starts from the definition of aerodynamic criteria such as total lift close to zero, the pitching moment sign and value consistent with road holding and stability, a reduced sensitivity to side wind, gradual variation of the cross sections, etc. Then, the presence of the wheels is taken into account in order to reduce their aerodynamic interference with the body, and to manage the wake mechanisms in order to recover the kinetic energy of the flow without fitting the body with a solid diffuser: in fact, this would increase the car length without contributing much to the usable space. Theoretical and experimental work leading to a new shape particularly short in the rear part and able to improve both the accomodation of passengers in the rear seats and the visibility outside - at present a major drawback of actual cars - are shown together with aerodynamic drag benefits. Other advantages resulting from the application of the method are finally discussed.