Controlled flow around a finite square cylinder through suction at the side and free-end leading edge

Abstract

The flow around a finite square cylinder with suction control at the side and a free-end leading edge is investigated through direct numerical simulations at a Reynolds number of 250. The absolute value of the ratio (Γ) between the suction velocity and the free-stream velocity is in the range of 0<Γ≤2. The results show that suction reduces the drag and fluctuating lift on the square cylinder. The optimal control effectiveness for reducing the fluctuating lift coefficient Cl′ and the average drag coefficient Cd¯ is achieved at Γ=0.375 and 0.75, respectively (Cl′ reduced by over 70% and Cd¯ reduced by nearly 20%). This is superior to the control effect achieved by active suction control only at the side leading edge. Compared to suction applied only at the side leading edge, adding suction at the free-end leading edge suppresses the flow separation on the top surface of the square cylinder. Moreover, with increasing suction ratios, the tornado-like Tip Vortex scale at the free-end of the square cylinder decreases, and the root mean square of streamwise velocity fluctuation at various spanwise planes decreases. Additionally, a data-driven balanced model-based dominant flow mode identification method is adopted to identify the dominant modes of the flow field at the z/d=0 plane at different suction ratios. The results show that suction can suppress the influence of the square cylinder on the far wake, and as the suction ratio increases, the area of the free flow expands.