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A comprehensive treatment of a new technique to measure vehicle aerodynamic response under side wind conditions is presented. In opposition to the traditional measurement technique of yawing the vehicle by rotating the turntable, the flow itself is continuously deflected by the Pininfarina Turbulence Generation System (TGS), while keeping still the vehicle under investigation. By using this new technique it is possible to assess the dynamic behavior of vehicles, with particular regard to side forces and yawing moment, in more realistic unsteady conditions opposed to the static setup of traditional measurements. In the first part of this work, the unsteady flow, generated by the TGS, is characterized both by means of 4-hole Cobra probe and stereo PIV measurements in empty and non-empty wind tunnel configuration. Some data acquired on the road will also be shown and compared with wind tunnel measurements.

Aeroacoustics of road vehicles is becoming more and more important as it directly affects the comfort of the passengers. The tests made in the wind tunnel, in low-turbulence flow conditions, show results that are qualitatively different from those measured on the road. To get a better understanding of this, Audi and Pininfarina decided to carry out a test campaign on some cars, both on the road and in the wind tunnel, in various turbulent flow conditions. In the case of road measurements, some typical turbulent flow conditions, like those caused by atmospheric wind and those produced by the traffic, have been investigated. Wind tunnel measurements have been performed both in the base wind tunnel (in Audi and in Pininfarina) and in the presence of turbulent flows generated, in the Pininfarina wind tunnel, by the Turbulence Generator System, already described in previous SAE papers [1,3,5,7].

The new Turbulence Generation System (TGS), presented in the SAE papers 2003-01-0430 and 2004-01-0807, is now systematically used to get a deeper insight in the aerodynamic and aeroacoustic behavior of passenger cars in a controlled high turbulence flow. The TGS itself is used to generate a flow with characteristics more similar to those encountered by a car when traveling on the road, either for the presence of natural wind or for the presence of upstream vehicles. A comparison is presented between tests performed in the low turbulence flow, i.e. base wind tunnel, and in the high turbulence flow, i.e. wind tunnel with TGS. In particular, results regarding the following aspects are presented: Car Lift in the presence of various TGS setups; Brake Disk Cooling; Interior Noise. For each one of these aspects, some time-averaged and some time-dependent values are presented.