Control of cylinder wake dynamics with symmetric synthetic jets near the flow separation points

This experimental study examines the flow control efficacy of symmetric synthetic jets (SSJs) on a circular cylinder wake at Re=2000, employing particle image velocimetry (PIV) to quantify wake characteristic, vortex dynamics and turbulent statistics. The SSJs, strategically positioned at the time-averaged flow separation points (θ=±90∘) with momentum coefficient Cμ=1.34, which corresponds to the SSJs Reynolds number Reu0¯=95, are frequency-modulated across three dimensionless actuation frequencies (fsj∗=fsj/f0= 1, 2 and 3). Results demonstrate that frequency-tuned momentum injection alters the wake structure through three frequency-dependent effects: The shedding pattern changes from 2 S to 2P; the near-wake recirculation and stagnation zones shrink; and vorticity is more confined near the cylinder, reducing downstream fluctuations. Lagrangian coherent structure (LCS) analysis shows that repelling LCSs move closer to the cylinder, while attracting LCSs converge toward y=0, consistent with a narrower wake. Reduction of the near-wake stagnation zone and recirculation region sizes indicates a progressive suppression as the SJs actuation frequency increases. Vorticity confinement in the immediate cylinder wake suppresses large-scale vortex development while promoting earlier roll-up near the cylinder and lowering velocity fluctuations downstream. The study establishes frequency-modulated SSJs as an analysis tool for multiscale wake control, offering two practical effects: stronger local mixing and weaker large-scale unsteadiness. These findings provide new insights into bluff body flow control strategies and their implications for regulating aerodynamic forces.