Effect of base blowing by a large-scale fluidic oscillator on the bistable wake behind a flat-back Ahmed body

Abstract

The dynamics of the wake behind a flat-back Ahmed body are modified using a large-scale fluidic oscillator, aiming at drag reduction and the reflectional symmetry breaking (RSB) mode suppression. In the present experiment, the sweeping jet (SWJ) actuator is integrated into the base of the bluff body such that its nozzle width corresponds to about 2/3 of the bluff body base width. The jet is sweeping in the horizontal plane, which coincides with the plane of the wake flow state switching due to the RSB mode. The impact of the SWJ actuator is evaluated for three different locations along the base's height, and for a range of blowing coefficients. The base suction coefficient is recorded from four pressure measurements at the base, while the drag coefficient is obtained from direct force and moment measurements. Particle image velocimetry of the near wake reveals the modifications of the mean flow, which elucidate on the changes in the base suction and drag coefficients. Both drag reduction and RSB mode suppression are achieved, however, not for the same blowing coefficient. The symmetrized wake yields a near Gaussian distribution of the base pressure gradients around zero in both gy and gz directions. This result is corroborated by the joint probability distributions of pitching and yawing moment fluctuations from force balance measurements.