Influence of the center cylinder on the flow characteristics of four- and five-cylinder arrays at subcritical Reynolds number

Abstract The three-dimensional flow around the four-cylinder and five-cylinder arrays are numerically studied at Re = 3900 by large eddy simulation (LES). By selecting eight spacing ratios (L/D = 2.0–7.0) and three incidence angles (α = 0°–45°), the influence of the center cylinder on the flow characteristics and interference effects of the four-cylinder array is discussed. Different spacing ratios can be divided into three categories with respect to flow regions of the multi-cylinder: small gap flow regime (L/D = 2.0–3.5), critical flow regime (L/D = 3.5–5.0) and large gap flow regime (L/D = 5.0–7.0). For cases with small spacing ratios, the influence of the center cylinder is very notable on the flow characteristics of the four-cylinder array. As the ratio increases, the influence of the center cylinder gradually decreases on the surrounding cylinders in the multi-cylinder array. On the other hand, the direction of the incoming flow also affects the flow characteristics of both four-cylinder and five-cylinder arrays. The development of the shear layer is strongly influenced by the center cylinder for the upstream cylinders at α = 45°. Boundary vortex flux components, flow characteristics and fluid force coefficients change significantly with adding the center cylinder for the four cylinders.