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Particle Image Velocimetry (PIV) is a recent measuring technique, which has been used up to now mainly by University Laboratories in small-scale wind tunnels and by Aeronautical Research Centers in small and large facilities. Its use in full-scale automotive testing is not common. It is not so easy, often rather difficult, due to a number of problems, sometimes of practical nature, sometime caused by technology limitations. This paper reports the results of some tests, carried out by CIRA (Centro Italiano Ricerche Aerospaziali) in the Pininfarina wind tunnel on a full-scale car, in the frame of the European Thematic Network “PIVNET”. A description of the test set up, of the instrumentation used for these tests, as well as an analysis of the advantages provided by this technique and of its present limitations, are reported. During the tests, in order to outline the potential of this measuring technique, some specific areas of the car flow field, have been investigated.

Aerodynamics of modern cars is usually investigated in condition of very low turbulence flow and zero yaw. Furthermore, the majority of the tests are often carried out in wind tunnels with fixed ground and static wheels. The effects of a more realistic flow simulation on the car underbody produced by the ground motion and the wheel rotation have been reported in the SAE paper 980031 presented at the 1998 Int’I SAE Congress. This parametric study was carried out in the Pininfarina wind tunnel, by using the Ground Effect Simulation System (“GESS”) built in 1995 and a full-scale simplified car model. This paper reports the follow up of this investigation. The same simplified car model and its underbody interchangeable underbody parts has been tested again, using the “GESS”.

The paper refers to a research program which is presently in progress at Pininfarina. It deals with a new ground effect simulation system for full-scale car testing in an automotive wind tunnel. This research program is carried out in the framework of the “Progetto Finalizzato Trasporti 2” of the Italian C.N.R. The first part of the paper makes an analysis of: The various ground effect simulation systems already existing in the world. The results which can be achieved using these systems. Their main limitations and drawbacks and some considerations about the possibility of using these systems for routine aerodynamic development work on full-scale vehicles. The second part of the paper describes the new Ground Effect Simulation System (GESS) which is presently in operation in the wind tunnel of the Pininfarina Aerodynamic and Aeroacoustic Research Center. Its layout is quite different from the ground effect simulation systems existing in other full-scale automotive wind tunnels.