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Aerodynamic drag of a modern car is generated mainly by underbody flows. A better understanding of these flows and of their interactions with the car underbody, may contribute to the future improvement of the car drag characteristics. This paper reports the results of a parametric study carried out in the Pininfarina wind tunnel, on a full scale simplified car model, by using the Ground Effect Simulation System built in 1995. The main aim of this study was to investigate the effect on the aerodynamic coefficients produced by important geometric changes which affect the flows under the car, in proximity of the ground, and are often difficult or impossible to be modified when tests are made on real cars. The model chosen for this research program is that defined by the SAE “Open Jet Interference Committee” as a reference model to be used for investigating wind tunnel interference and for comparison between wind tunnels. In particular it has no wheels.

Modern vehicles require a low aerodynamic drag to minimize fuel consumption. A not negligible share of the overall CD-value of a vehicle is produced by the engine compartment air flow. Therefore this share has also to be optimized. Furthermore, customer wishes for higher powered engines as well as for more safety and comfort result in more tightly packed engine compartments. Even the reduction of pass-by-noise required by legal reasons is often achieved with the help of underbody covers which in turn affect the engine compartment flow. All these items may lead to rising underhood temperatures. To reduce the development time of new vehicles, numerical simulations of engine compartment air flow are more and more used to predict high temperature fields and to show ways to develop suitable remedies in the concept phase of the vehicle development. The experimental basis for such codes is provided by aerodynamic investigations in a wind tunnel.