Reynolds Number Effect on Flow Classification Behind Two Staggered Cylinders

This work aims to investigate based on the Strouhal number St and the flow structure, the dependence of flow classification on the Reynolds number Re in the wake of two staggered cylinders, with Re varying from 1.5 × 10³ to 2.0 × 10⁴. The cylinder center-to-center pitch, P ^*  = P/d examined is 1.2–6.0 (d is the cylinder diameter), and the angle (α) between the incident flow and the line through the cylinder centers is 0°–90°. Two single hotwires were used to measure simultaneously the St behind each of the two cylinders at streamwise positions from x ^*  = x/d = 2.5–15. While the present data reconfirms the flow structure modes previously reported, the dependence of the flow modes on P ^* and α exhibits an appreciable dependence on Re. The observation is connected to the Re effect on the generic features of a two-cylinder wake such as flow separation, boundary layer thickness, gap flow deflection, and vortex formation length.