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An analytical model is used to compare the influence of aerodynamic parameters on vehicle dynamics at high speeds (typically 180 km/h) to the influence of other important vehicle characteristics. Typical driving conditions considered are fast highway driving, braking, and driving in a cross wind. Some experimental results are presented in addition. The results show that a low overall lift level with a positive pitch moment is desirable for good handling characteristics. They also show that observed differences of the aerodynamic data on production cars are less influential on crosswind sensitivity compared with certain other vehicle characteristics, such as center of gravity position. The control of the important aerodynamic parameters influencing vehicle dynamics, such as lift and yaw-moment coefficients, is described in some detail. Ine behavior of these aerodynamic parameters for low-drag cars is also discussed.

Among the ways to reduce the resistance to motion and, in turn, improve fuel economy for future mass-produced passenger cars, the reduction of aerodynamic drag is the most promising. It is shown that drag reductions of 2 5 % to 35 % are achievable in future mass-produced passenger cars. This indicates that aerodynamics alone can provide a 10 % to 15 % fuel economy improvement in future passenger cars. The development procedures, and the shape and design characteristics which lead to such mentioned drag reductions are described and analyzed in some detail.

As part of the general program for comparing leading European automotive wind tunnels, three reference cars derived by Volkswagen (VW), Pininfarina (PF) and FIAT Research Center (CRT) from production models, were tested in different configurations. This report contains the result of tests carried out on a CRF reference car in CRF, VW, DB and PF wind tunnels as well as on the road. The wind tunnel tests of the car in 7 different configurations show a fairly good agreement particularly for the drag coefficients measured in the various tunnels. Road tests were carried out with the car in three configurations at constant speed (measuring front and rear axle lift, body pressure and visualising the wake) and in coast-down (measuring aerodynamic resistance). The results obtained proved that road driving conditions with no side wind or turbulence are correctly simulated in wind tunnel tests.

A correlation test program between four European full-scale automotive wind tunnels has been performed on a passenger car modified in five different rear-end configurations which cover most of the present passenger cars. The aim of this program was mainly to evaluate to what extent the aerodynamic drag coefficients, measured in these four different wind tunnels, are reliable and therefore can be used for technical or legislative purposes. The correlation program was extended also to the other force coefficients, that is, lift and side forces, and to the pressure distributions. Tests were carried out at different speeds from 90 to 150 Km/h and at different yaw angles β from − 50° to + 50°. The comparison shows a generally good agreement between the results of these four tunnels, the differences for tests at β = 0° being, in terms of the standard deviations, in the order of ± 2% as regards the drag coefficient, ± 0.025 and ± 0.011 as regards the front and rear lifts.

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.

Comparative aerodynamic force measurements on a full scale notchback type vehicle have been performed between six European companies operating prominent full scale automotive wind tunnel facilities. The results obtained with 8 different vehicle configurations show a remarkably good correlation between the drag coefficients measured in the various wind tunnels. Pressure distributions also show an acceptable agreement. The comparison of front axle lift measurements revealed differences between the various wind tunnels; these differences are partly explainable. Six component measurements also show a satisfactory correlation between the various wind tunnels except where lift does contribute to the forces or moments. Suggestions to extend these correlation tests are presented.

Advanced experimental techniques have been developed for application in the Volkswagen automotive wind tunnels. Such procedures are: laser-Doppler anemometry (LDA) for detailed flow-field measurements; laser-light-sheet technique for flow visualization; probe positioning by a robot; and frontal-area determination by a laser-reflection system. Experiences with these advanced experimental techniques are reported in some detail. Examples of test results are shown, and the different application areas as well as the usefulness of the various methods for the advancement of automotive aerodynamics are discussed.