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

Flow past two wall-mounted square cylinders in staggered arrangement is simulated through direct numerical simulation to investigate the effects of the degree of staggering on the wake and forces compared to the tandem arrangement. Numerical simulations are conducted for a constant Reynolds number of 500, height to width ratio H = 4, staggered distance to diameter ratios S = 0.5 and 1, and gap to width ratios G in the range from 1 to 8. It is found that moving the downstream cylinder sideway for S = 0.5 and 1 changes flow features and force coefficient significantly. At small gaps of G = 1 to 3, the shear layer from one side of the upstream cylinder is trapped into the gap. In addition, a strong horseshoe vortex in front of the downstream cylinder is found for all the gaps at S = 0.5 and 1, but not found at S = 0. The friction velocity on the plane boundary caused by the horseshoe vortex of the downstream cylinder is greater than that of a single cylinder at S = 1 and G = 1 to 8 and at S = 0.5 and G = 2 to 5. At G = 1 to 3, vortex shedding is caused by the trapped flow into the gap on one side of the downstream cylinder and by the approaching flow on another side. The negative mean drag coefficient at small gaps was found in the tandem arrangement case, but not found at S = 0.5 and 1.