Large eddy simulation of flow around two tandem circular cylinders at a Reynolds number of 3900

This paper investigates the flow dynamics around two tandem circular cylinders with different spacing ratios (L/D, L is the center-to-center spacing and D is the cylinder diameter) under a subcritical Reynolds number of 3900. Large eddy simulations are conducted using a well-validated three-dimensional (3D) numerical model Zeng et al., [Phys. Fluids 35, 035102 (2023)] at eleven spacing ratios (L/D = 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, and 7). As the spacing ratio (L/D) increases, the flow field around the cylinders sequentially exhibits the following wake regimes: the extended-body regime (L/D = 1.2), the reattachment regime (L/D = 1.5–4), the transitional regime (L/D = 4.5), and the co-shedding regime (L/D = 5–7). The characteristics of each regime were qualitatively analyzed using parameters such as the hydrodynamic coefficients, the circumferential pressure coefficient, and the vortex shedding frequency. For the reattachment regime, the shear layer separation points and the reattachment points on the downstream cylinder are examined. Based on the instantaneous vorticity field, the reattachment regime is further classified into the alternate impact mode and the alternate attachment mode. In the co-shedding regime, there is a phase lag between the vortex shedding of the two cylinders, and it is found that this phase lag increases linearly with the spacing ratio.