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This paper provides a method that corrects errors induced by the empty-tunnel pressure distribution in the aerodynamic forces and moments measured on an automobile in a wind tunnel. The errors are a result of wake distortion caused by the gradient in pressure over the wake. The method is applicable to open-jet and closed-wall wind tunnels. However, the primary focus is on the open tunnel because its short test-section length commonly results in this wake interference. The work is a continuation of a previous paper [4] that treated drag only at zero yaw angle. The current paper extends the correction to the remaining forces, moments and model surface pressures at all yaw angles. It is shown that the use of a second measurement in the wind tunnel, made with a perturbed pressure distribution, provides sufficient information for an accurate correction. The perturbation in pressure distribution can be achieved by extending flaps into the collector flow.

The results of comparative aerodynamic force measurements on a full-scale notchback-type vehicle, performed between 6 European companies operating full-scale automotive wind tunnels, were published in the SAE Paper 800140. Correlation tests with the same vehicle have been extended to 2 further European and 3 North American wind tunnels. First the geometry, the design and the flow data of the different wind tunnels is compared. The facilities compared include wind tunnels with open-test-sections, closed-test-sections and one tunnel with slotted side walls. The comparison of results, especially for drag coefficients, show that the correlation between the differently designed wind tunnels is reasonable. Problems of blockage correction are briefly discussed. The comparison tests furthermore revealed that careful design of the wheel pads and blockage corrections for lift seem to be very influential in achieving reasonable lift correlations. Six-component measurements show similar problems.