Streamwise sinusoidal flow over two identical tandem circular cylinders

Abstract

This study conducts three-dimensional large eddy simulations at a subcritical Reynolds number of 103 to investigate the effects of sinusoidal streamwise flow on the flow structure, Strouhal number, and aerodynamic forces of two tandem circular cylinders. The center-to-center spacing L between the two cylinders is fixed at 3.5D, where D is the cylinder diameter. The velocity U of sinusoidal streamwise flow is set as U* = U/U0 = 1 + A*sin(2π(f*U0/D)t), where A* denotes the velocity amplitude ratio, and f* ((fuD/U0)/St0) denotes the non-dimensional frequency of sinusoidal flow, with fu being the frequency of sinusoidal flow and St0 being the Strouhal number of two tandem cylinders with L/D = 3.5 under the uniform approaching flow. The results show that the variations of f* (0–2.67) and A* (0–0.25) lead to the generation of not only the reattachment and coshedding flows independently but also their joint flow involving intermittent occurrences of the reattachment and coshedding flows. A map of the dependence of the flow structure on f* and A* is presented, marking the borders of various flow patterns in the f* − A* plane. Flow separation, Strouhal number, and aerodynamic forces on the two cylinders are found to be sensitive to f* and A*, exhibiting distinct variations following the flow structures. A time-frequency analysis of the bistable pattern is presented, identifying the two distinct vortex-shedding frequencies and confirming the time dependence and bi-stability of the bistable flow.