FLOW CONTROL OF A CYLINDER WAKE USING SYNTHETIC JET TECHNOLOGY

Synthetic jets are zero-net mass flux flows that have been recently used in a wide range of flow control applications, among which the control of bluff body wakes. An optimal control is based on an appropriate tuning of the involved parameters, which implies knowledge of the effects of such parameters on the flow field. The present work reports on an experimental investigation of the active open-loop control of a cylinder wake at Reynolds number equal to 4600 using a slot synthetic jet located at the rear stagnation point. Three values of f+ (0.49, 0.98 and 1.96) are considered and, for each of them, Cµ is varied among as many different values (5.4%, 10.8% and 21.6%) for a total of five investigated Reynolds numbers ratio R (1.0, 2.0, 4.0, 8.1 and 16.4). The flow field in the cylinder wake is found to be highly sensitive to the variations of f+ and Cµ. By increasing Cµ. and/or f+ the extent of the time-mean recirculation region is observed to decrease. Furthermore, the cylinder wake can exhibit a symmetric or an asymmetric behavior depending on the R. Indeed, at high Reynolds numbers ratio R, the cylinder wake shows a symmetric behavior because of a strong synthetic jet which stops the evolution of the shear layer instability leading to a synchronization of the vortex shedding with the synthetic jet Differently, at low R, the evolution of the cylinder wake shows the classic asymmetric behavior.