1985-02-01

Full-Scale, Ort-Road Study of the Effect of Automobile Shape on its Aerodynamic Characteristics, and Comparison with Small-Scale Wind Tunnel Results 850287

The design of passenger vehicles for improved aerodynamic characteristics will result in reduced fuel consumption and better road handling during high-speed driving. In this research, techniques were developed to measure the aerodynamic drag and lift forces acting on a full-scale vehicle under road conditions and then were compared with results obtained on reduced-scale models in a wind tunnel. A number of configurations which characterize common vehicle forms were investigated for their effect on aerodynamic efficiency and fuel consumption, Experimental speeds were between 70 and 110 km/h, these being representative of highway driving conditions.
A typical passenger vehicle of the three-box type was selected for the experiments, and its exterior form was altered by means of attaching various configurations to its front, rear, and underbody portions. These additions transformed the original vehicle into a “fast-back” and “station wagon,” and were used in combination with underbody alterations, such as front spoiler, side skirts, and smooth underbody. During road experiments, drag force was measured by means of a telemetric system receiving data on drive-shaft strains, whereas lift forces were measured by relative vertical displacements in the front and rear suspensions.
Statistical analyses showed that the different configurations had a significant effect on the aerodynamic forces. The change in configurations brought about a maximum reduction in drag coefficient (CD) of 51%, relative to the original vehicle. As a result, fuel consumption was reduced by 13% (at 110 km/h). Lift forces dropped by as much as 47%. The most effective components were a smooth underbody and a “fast-back” form for drag, and a smooth underbody and front spoiler for low lift. Results of the road experiments showed a reasonable correlation with those obtained using reduced-scale models in a wind tunnel.

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