Square cylinder flow controlled by a synthetic jet at one leading edge

Shear layers separating from opposite sides of a bluff body are inherently connected with near wake flow structures; interfering one of the shear layers may lead to dramatic changes in the near wake flow and fluid forces on the bluff body. Being motivated by this, we investigate the square cylinder flow disturbed by a synthetic jet at one leading edge of the cylinder. Large-eddy simulations are conducted at a Reynolds number Re = 5.0 × 103. The synthetic jet is driven by a sine function with frequency f j = 0-1.65 f o and magnitude V j, o = 0-1.0 U o (corresponding to momentum coefficient C μ = 0-1.01%), where U o is the free stream velocity, and f o is the dominant vortex-shedding frequency of the uncontrolled flow. The results indicate a strong dependence of fluid forces and flow structures on C μ and f j. Time-mean drag (C ¯ d) and fluctuating lift (C l, rms) are significantly reduced at high f j (>1.21 f o) and C μ (>0.25%), compared to those of the uncontrolled flow; the maximum reductions in C ¯ d and C l, rms are up to 39% and 33%, respectively, at the highest f j = 1.65 f o and C μ = 1.01% considered presently. Modifications of the near wake flows by the synthetic jet perturbations of different frequencies are discussed based on instantaneous, time-mean, and phased-averaged results. A high efficiency is attained by the present control strategy.