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Wheels and wheelhouses are a significant source of aerodynamic drag on passenger cars. The use of air jets, in the form of an air curtain, to smooth the airflow around front wheel housings on cars has become common practice, as it produces a small drag benefit. This paper reports an initial small-scale wind tunnel study of an air jet employed as an effective wheel spoiler to reduce the drag produced by the front wheels and wheel housings of passenger cars. For this investigation, the air jet was created using an external compressed-air supply and was applied to a highly simplified car body shape. The data presented suggest that the air jet has some potential as a drag-reduction device.

The aerodynamic drag reduction of road vehicles is of continuing interest. The drag arising from the rear surfaces is usually the dominant component, but this can be alleviated by the tapering of the rear body. The effects on the aerodynamic characteristics of a simple body from adding an elongated tapered tail have been investigated in a wind tunnel experiment. The streamlined tail consists of a constant rear body side taper added to a constant upper body taper. The results have been compared with an earlier study of the same body with upper body tapering only. The effects of truncating the long tail are explored. Adding the planform tapering reduces the impact of the slant edge vortices, and drag and lift are substantially reduced. The lateral aerodynamic characteristics are largely unaffected.

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.

A drag coefficient, which is representative of the drag of a car undergoing a particular drive cycle, known as the cycle-averaged-drag coefficient, has been previously developed. It was derived for different drive cycles using mean values for the natural wind. It assumed terrain dependent wind velocities based on the Weibull function, equi-probable wind direction and shear effects. It did not, however, include any effects of turbulence in the natural wind. Some recent research using active vanes in the wind tunnel to generate turbulence has suggested that the effect on drag can be evaluated from the quasi steady wind inputs. On this basis a simple quasi-steady theory for the effect of turbulence on car drag is developed and applied to predicting the cycle-averaged-drag coefficient for a range of cars of different types. The drag is always increased by the turbulence but in all cases is relatively small. Turbulence is also present when driving in traffic, but traffic also introduces a velocity deficit, which reduces drag. By making certain assumptions about traffic flow, a crude traffic model is developed and the impact of traffic on the cycle-averaged-drag has been derived. It is found that the combination of natural wind turbulence and the effects of traffic results in very small changes to the cycle-averaged-drag coefficient.