Abstract
The car aerodynamicist developing passenger cars is primarily interested in reducing aerodynamic drag. Considerably less attention is paid to the lift characteristics except in the case of high-performance cars. Lift, however, can have an effect on both performance and stability, even at moderate speeds. In this paper, the basic shape features which affect lift and the lift distribution, as determined from the axle loads, are examined from wind tunnel tests on various small-scale bodies representing passenger cars. In most cases, the effects of yaw are also considered. The front-end shape is found to have very little effect on overall lift, although it can influence the lift distribution. The shape of the rear end of the car, however, is shown to be highly influential on the lift. The add-on components and other features can have a significant effect on the lift characteristics of real passenger cars and are briefly discussed. The increase in lift at yaw is, surprisingly, almost independent of shape, as shown for the simple bodies. This characteristic is less pronounced on real passenger cars but lift increase at yaw is shown to rise with vehicle length.
Highlights
Shape Factors InfluencingThe primary role of the aerodynamics development engineer working on passenger car design is typically to reduce drag without compromising stability or refinement
In an ideal development process, shape changes which reduce drag would result in desirable overall lift and distribution of lift, but this rarely occurs in practice and compromises will be required
The results shown in this paper suggest that overall lift is fairly insensitive to major shape changes, except at the rear of the car
Summary
Shape Factors InfluencingThe primary role of the aerodynamics development engineer working on passenger car design is typically to reduce drag without compromising stability or refinement. Aerodynamic lift has a strong effect on car stability at high vehicle speeds. For the front-end shape changes, with the exception of the vertical windscreen case, the incidence is identical and the camber is very similar, implying negligible change in lift, which is shown by the data. In the case of the rear-end shape changes, an increasing slant angle increases both camber and incidence, which suggests that lift will increase, as shown by the results for pre-critical slant angles. It should be noted, that the lift is enhanced by the slant edge vortices, which are not considered in the simple theory. Camber is increased while incidence is unchanged, which suggests a lift increase, as shown by the data
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