Numerical study of the flow past two wall-mounted finite-length square cylinders in tandem arrangement

Flow past two wall-mounted square cylinders in a tandem arrangement are simulated through direct numerical simulation to investigate the effects of the gap between the two cylinders on the wake. Numerical simulations are conducted for a constant Reynolds number of 500, height to width length ratio H = 4, and gap to width ratios of G = 1 to 8 with an interval of 1. The flow in the wake of the downstream cylinder is found to be significantly affected by the free shear layers from the top and sides of the upstream cylinder. At G = 1 and 2, the free-shear layer generated from the upstream cylinder reattaches the top surface of the downstream cylinder and further develops into a downwash behind the downstream cylinder. At G = 3 to 8, the downwash behind the downstream cylinder disappears because flow separation from the top upstream edge of the downstream cylinder does not occur for G = 3 to 6 and is very weak for G = 7 and 8. The disappearance of downwash in the wake of the downstream cylinder further results in very weak variation of flow along the span of the downstream cylinder. The single, reattachment, and binary wake modes at the mid-span of the cylinder occur at G = (1 and 2), (3 and 4), and (5 and above), respectively