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Starting from September 2006, a new Moving Ground System is in operation in the Pininfarina wind tunnel. This system has replaced the old one, in service since 1995, which was the first in the world with a narrow belt integrated into the balance/turntable. The new Moving Ground System has a number of improvements, namely: An increased top speed, up to 250 Km/h A much longer and slightly wider central belt, e.g. it is 6.7 m long and 1.1 m wide Two additional belts at the sides A number of innovative features that make this system well suited for testing racing cars. In particular, this system has two additional belts at the sides of the central belt to cover the part of the ground that is under the car front end, for a width of 2.5 m and a length of 1.5 m. This feature, patented by Pininfarina, greatly improves the simulation of the flow under the front wing of a Formula 1 car or under the front end of a racing car. Details are shown in the paper.

Starting from September 2006, a new Moving Ground System is in operation in the Pininfarina wind tunnel. This system has replaced the old one, in service since 1995, which was the first in the world with a narrow belt integrated into the balance/turntable. The new Moving Ground System has a number of improvements, namely: - An increased top speed, up to 250 Km/h. - A much longer and slightly wider central belt, e.g. it is 6.7 m long and 1.1 m wide. - Two additional belts at the sides. - A number of innovative features that make this system well suited for testing racing cars. In particular, this system has two additional belts at the sides of the central belt to cover the part of the ground that is under the car front end, for a width of 2.5 m and a length of 1.5 m. This feature, patented by Pininfarina, greatly improves the simulation of the flow under the front wing of a Formula 1 car or under the front end of a racing car. Details are shown in the paper.

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.

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.

Aeroacoustics is playing an increasing role in the development of new passenger cars. However, most existing wind tunnels, with few recent exceptions, have been designed and built with little or no attention to their aeroacoustic aspects. Building new wind tunnels with excellent low noise levels is technically feasible today, however it is not often justifiable from an economic standpoint. In the case of the Pininfarina wind tunnel, built in 1972 without any specific noise target, a decision was taken in 1984 to progressively upgrade the facility and the acoustic measuring techniques. A target of reaching a background noise level low enough to allow satisfactory acoustic development work on new cars, with the contemporary use of more modern measuring techniques, was established. This decision implicitly assumed that, to do this development work, it is not necessary to reach the very low noise levels of a pure acoustic wind tunnel.

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.

The paper summarizes various flow-field survey techniques which have been developed at Pininfarina in recent years to analyse the flow field around cars in the wind tunnel. Some of these techniques are now fully integrated into wind tunnel everyday work. Among them, the “14-hole probe” technique has been recently upgraded by the development of two new “micro-drag” and “vorticity” maps. The paper describes the most recent advances in these techniques and, mainly, the strategy employed in the Pininfarina wind tunnel to maximize the usefulness of the information obtained about a car flow-field with a minimum of wind tunnel run-time. The core of this strategy is the choice of a carefully chosen set of planar surveys carried out around the car in the most critical areas, so that a complete overview of the whole car flow-field can be achieved.

This paper illustrates an advanced technique recently introduced in the Pininfarina wind tunnel for surveying the flow field of full-scale passenger cars. The technique is based upon the use of a non-nulling seven-hole probe, which is traversed continuously by a fast traversing system. The traversing system moves in the flow field under computer control. Planar surfaces of various preselected sizes can be surveyed with corresponding wind tunnel run times ranging from 5 to 40 minutes. As a result of a single planar survey, local pressures and velocities are mapped on a computer colour-display output. Usually, four colour maps are generated to show and summarize the distribution of total and static-pressure coefficients and total and cross-flow velocities. This technique is used mainly to investigate body wakes. Several examples regarding passenger cars or models, as well as an isolated formula-one type rear wing, are reported.

Flow field mapping techniques have been regarded with great interest in recent years. They are an important tool for investigating flow characteristics around new car models during their development in the wind tunnel. A short summary of previous techniques developed by Pininfarina, since 1982, is reported. Latest developments are then shown, which include: A new probe, capable of measuring local pressures and velocities both in straight and reverse flows. It utilizes a “fourteen-hole” pattern which overcomes most of the limitations previously found with “seven-hole” probes. The upgrading of the wind tunnel traversing system, both in its hardware and software components. Probe traversing velocities up to 120 mm/sec are now commonly used during the pressure data acquisition. Furthermore pressures and velocities may now be mapped along planar surfaces being horizontal or vertical, transversal or longitudinal, in front of, at the side of, or behind the car model.

The flow-field mapping technique previously developed in the Pininfarina wind tunnel has further evolved during 1986. The former technique (1985), based on the use of a “seven-hole” probe, had two main limitations: poor sensitivity at low speed (<8 m/sec.) incapability of measuring at flow angles greater than +− 70° Both these conditions often occur inside the near-wakes of passenger-car models. Therefore, wake maps (velocities and pressures) made in the past were largely incomplete in their inner parts. The new probe has a double “seven-hole” pattern and its performance exceeds that of two “seven-hole” probes used separately. It was developed during the fourth year of a research program aimed at providing new experimental information on reverse flows in automobile wakes, for use in developing improved computational fluid dynamic (CFD) techniques for automobiles. Reverse flows inside the near-wake of three full-scale squareback car models were investigated.

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”.