Unsteady Wakes of Three Dimensional Bodies

The effect of a splitter plate on the near wake of a three dimensional bluff body in proximity to a ground plane was 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. It was determined that the splitter plate raised the spatially averaged mean pressure on the base by 15% when placed one fourth model height below the top of the base. The splitter plate also decreased the spatially averaged fluctuating pressure level between 13% and 31%, but the decrease in fluctuating pressure level was not necessarily accompanied by a decrease in drag. These measurements indicate that the aerodynamic drag of bluff bodies is related to unsteady effects in the wake. The near wake structure behind the bluff body was investigated using flow visualization and two hot wire anemometry probes and cross-correlating the velocity signals. The development of a periodic flow structure that was one half the model height in size was examined.