VIV of twin square cylinders in various configurations at a low Reynolds number

Abstract

Vortex-induced vibration (VIV) of twin square cylinders is numerically investigated at Re = 150 with tandem, staggered and side-by-side configurations. Three VIV categories are identified due to dynamic responses, flow-induced forces and flow fields. For Case-Ⅰ (α = 0°), two cylinders only display the typical synchronization region (the reduced velocity of the synchronization region, Vr ≈ 5–6). The maximum transverse amplitudes of twin cylinders are 2 times and 2.4 times that of the single one (Ay,max = 0.3B, B is cylinders' characteristic length), respectively. There is also sizable streamwise oscillation for Cylinder-2 (Ax,max = 0.48B). Compared to Case-Ⅰ, streamwise and transverse amplitudes of twin cylinders systematically rise for Case-Ⅱ (α = 15°, 30°), where Ay,max and Ax,max of two cylinders is approximately 1.9 times and 2.9 times those in Case-Ⅰ, respectively. Two cylinders exhibit not only a typical synchronization region (Vr ≈ 5–6) but also a non-typical synchronization region at high Vr ≈ 10–12. Unlike the typical one, Cylinder-2 within the non-typical region shows stronger vortexes, more pronounced vibrations and lower fluctuating lift. For Case-Ⅲ (α = 45°–90°), the flow interference of twin square cylinders mainly occurs in the wake area and marginally affects the dynamic responses. The VIV characteristics of twin cylinders are similar to those of an isolated cylinder.