Effects of Synthetic jets on a D-Shaped Cylinder wake at a Subcritical Reynolds Number

Effects of synthetic jets on the wake of a D-shaped cylinder is investigated experimentally at a Reynolds number Re_H= 47,000, based on incoming free-stream velocity and the cylinder height (H). The synthetic jets are introduced immediately from the upper and lower trailing edges of the cylinder. The upper and lower synthetic jets are operated in an in-phase or anti-phase mode, and at a momentum ratio C_μ= 1.0% and perturbation frequency St_A= 0.11 ?0.37. The cylinder wake with perturbation is examined in detail and compared with that without, based on smoke-wire flow visualization, pressure transducer and hotwire rake measurements, and data analyses of spectra, tempo-spatial cross-correlation and proper orthogonal decomposition (POD). Large-scale vortical structures in the cylinder wake are significantly modified by the synthetic jets perturbations, exhibiting symmetric or asymmetric patterns, depending on the perturbation frequency and phase relationship of the synthetic jets. These observations are internally correlated with the drag force variations.