Generation of a Controlled Level of Turbulence in the Pininfarina Wind Tunnel for the Measurement of Unsteady Aerodynamics and Aeroacoustics

In 1995, in order to bring the wind tunnel simulation as close as possible to the road condition, Pininfarina integrated the “rolling road” with the balance system and provided a means to rotate the car wheels. That was certainly an important first step to improve the airflow simulation of a vehicle moving on the road. However, to reproduce real on-road flow conditions in the wind tunnel, it is necessary to do a second equally important step. That is, it is necessary to be able to reproduce turbulent flow conditions similar to what a vehicle usually experiences on the road. In fact, it is known from previous works that for most of the time, a road vehicle is moving in the presence of turbulent flows, generated either by some natural low-speed wind or by other vehicles moving upstream. These flow conditions are very different from the almost perfect low-turbulence flow that is typical of modern automotive wind tunnels. The resultant car flow field is different, for both aerodynamics and aeroacoustics.

In the first part, the paper reports on some considerations regarding turbulent flows that are statistically more interesting to reproduce in the wind tunnel. Then it describes the active system built in the full-scale wind tunnel to generate a controlled level of turbulence. Finally, it deals with the measuring techniques that are used to investigate these unsteady flows and presents a few examples of aerodynamic and aeroacoustic measurements carried out in the new flow condition.