Measurements in the Unsteady Near Wakes of Ground Vehicle Bodies

The effect of rear splitter plates and base cavities on the near wake behind a ground vehicle body above a moving ground plane were studied. Static pressure taps on the base of the body were used to measure both the mean and fluctuating pressures acting on the model base. Hot wire anemometry and flow visualization were used to study the effect of splitter plates and cavities on the near wake velocity field. The effects of varying ground clearance and of the moving ground on the base pressure were also studied.

It was determined that some splitter plate configurations affect the base pressure distribution by forming a low pressure vortex on one side of the plate with high pressure fluctuations and altering the flow on the opposite side of the plate to raise the mean pressure. The suction region could be eliminated by moving the splitter plate to the model edge to form a side of a cavity. A full four sided cavity was able to increase the overall base pressure by 11% on the model. The velocity fluctuations in the near wake decreased up to 50% with the use of a cavity. The base pressure distribution is not significantly affected by ground clearance if a moving ground plane is employed. These experiments indicate that the aerodynamic drag of bluff bodies is related to unsteady effects in the near wake.