Bluff body drag control by boundary layer disturbances

The experimental results are presented for the influence of thin plates and dimples arranged over the upper surface of a coach model on base pressure variations, turbulent wake characteristics, and body drag. The influence of the plate height, the plate spacing, the attack angle, and the distance from the plate trailing edge to the model base on pressure distributions over the model and its back panel are studied. It is shown that rather small disturbances of the boundary layer by plates cause the base pressure to increase up to 6% and model drag to decrease by as much as 3%. However, the effect of the dimples on the base pressure appears to be much less.