Flow around two square cylinders near a wall

A numerical study is conducted on flow over two staggered cylinders near a plane wall. The downstream cylinder (DC) is square, of height D, positioned near a plane wall with a gap height of 0.5D. The upstream cylinder (UC) is also square, with height d = 0.5D and 1.0D. For both d values, the UC gap height L is varied from L* (=L/D) = 0.1 to 3.0, and the streamwise spacing S between the UC and DC is varied as S* (=S/D) = 0.5–7.0. We focus on the effect of L*, S*, and d/D on the flow physics and aerodynamic forces on the DC. Six distinct flow patterns (namely, I, II, III, IV, V, and VI) are identified. The positive shear layer of the UC has profound effects on the dynamics of the DC flow. The Strouhal number and forces are strongly correlated with upstream vortices, particularly at lower spacing ratios in patterns II and V. For unsteady flow conditions, both cylinders exhibit identical vortex shedding frequencies for all flow patterns, except in pattern V when d/D = 1.0. The optimal UC position (L*, S*) is identified for minimum mean drag and fluctuating lift coefficients.