Car Underside, Upperbody and Engine Cooling System Interactions-and Their Contributions to Aerodynamic Drag

Automotive aerodynamic resistance is going lower and lower. New cars have a Cx near 0.30 and the trend is to reduce the drag even further. At this level the contributions of the car underside, wheel cavities and engine-cooling-system play an important role in the total drag.

This paper shows relevant results from wind tunnel tests on a 1/1 scale model equipped with internal balances which allow measurement of the individual drag contributions from the car underside and upper body. Total drag was measured with the wind tunnel balance. The resistance of the engine-cooling-system was directly measured, and compared with the value obtained from the difference in the car total drag when tested with and without the radiator-intake sealed.

Test results also show effect and interactions due to configuration changes.

The model's aerodynamic flow field was examined throught surface-pressure distributions and flow visualization; wake surveys, airflow between the model underside and the wind tunnel floor, and base pressures have also been investigated.