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The aerodynamic development of a convertible passenger car requires the optimization of additional characteristics, when compared to those which are considered for normal passenger cars.

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.