Drag of a D-shaped bluff body under small amplitude harmonic actuation

Open-loop flow control method was used to affect the development of a turbulent wake behind a D-shaped bluff body. Loud speakers were embedded inside the bluff body to produce two zero-net-mass-flux jets through 2 mm-wide span-wise slots located along the upper and lower edges on the rear wall. The drag forces for different actuation amplitudes (CμCμ, the ratio between the momentum of the actuating jets and the moment deficit caused by the bluff body) and frequencies (StA) were examined. The effects of the phase difference in the two jets (0 and π) were also studied. It was found that when CμCμ was 0.1%, a drag reduction up to 5% was achieved when the velocities of the two jets varied in phase at a frequency of StA=0.16. When the velocities of the two jets varied π out of phase, significant drag increase was observed.