Fluid-structureinteraction of four rigidly-connected square cylinders in steady flow

Abstract

Dynamic responses of four rigidly-connected square cylinders in a square configuration subjected to two-dimensional steady flow of a constant property Newtonian fluid were investigated numerically. The focus of the present study is to investigate the effects of the angle of attack α on the dynamic responses by varying α from 0 • to 15 • in intervals of 2.5 • at a fixed L = 4 (L is the non-dimensional center-to-center distance between two adjacent square cylinders, normalized by the side length of the square cylinder B). For each α, the reduced velocity (Vr) ranges from 1 to 40. The Reynolds number Re, mass ratio m * and structural damping ratio ζ maintain constants of 180, 10 and 0, respectively. Numerical results show that the angle of attack α has a significant influence on the dynamic response. When α ≤ 5 • , galloping occurs in addition to vortex-induced vibration (VIV), while it weakens for α = 7.5 • and 10 • , and finally disappears as α = 12.5 • and 15 • , leaving only VIV response. The effects of L on the responses of the four-square-cylinder oscillating system were also examined for Re = 180, Vr = 40, and α = 2.5 •. Numerical results show that L affects not only the response displacement but also the vortex shedding mode. Galloping with large response amplitude can happen at either large L = 4 or small L = 1.5 and 2. The response amplitude is relatively small as 2.5 ≤ L ≤ 3.5 due to the influence of the flow in the gap between the square cylinders. For the particular case of L = 3.5, a combined vortex shedding mode is identified, where the vortex shedding from the top row square cylinders behaves as that from an elongated single body while the vortex shedding from the bottom row cylinders presents a co-shedding mode.