Large eddy simulation of flow over a square cylinder with synthetic jets

Three-dimensional large eddy simulation is performed in the present study to analyze the control efficacy of synthetic jets on flow over a square cylinder in Re=180. Synthetic jets actuated by square, sinusoidal, bi-frequency, and varying duty-cycle signals are applied on the rear surface of the square cylinder in simulation. The vortex shedding pattern and streamwise vortical structures are investigated to assess the control effect of the synthetic jets. It is demonstrated that the control effectiveness can be improved with the characteristic momentum Msignal of synthetic jets. For signals with relatively low characteristic momentum, such as the square and sinusoidal signals, synthetic jets cannot fully control the wake. Dual alternating deflections of jet vortex pairs, along with 1/4fe frequency components, persist in the wake. Conversely, the higher-momentum signals, like bi-frequency and varying duty-cycle, generate stronger jets, eliminating deflection and synchronizing wake shedding at the excitation frequency. Tongue-like secondary streamwise vortices with a spanwise wavelength of 5.1D are observed in the wake without control. The application of synthetic jets suppresses the streamwise structures and improves the two-dimensionality in the spanwise direction. For low-momentum synthetic jets, antisymmetric Kármán vortices persist, but with improved spanwise uniformity, whereas high-momentum jets fully dominate the wake, suppressing shear-layer instabilities. The findings highlight the potential of optimized synthetic jet signals for effective wake flow control.