Mass ratio effect on vortex-induced vibration for two tandem square cylinders at a low Reynolds number

Abstract

A numerical simulation study is conducted to investigate the effect of the mass ratio (m* = 3, 10, and 20) on vortex-induced vibration (VIV) of two tandem square cylinders at Re = 150. In this study, we mainly focus on the mass ratio effect on the vibration response, force characteristics, wake mode pattern, and fluid–structure-interaction (FSI) mechanism. The results show that mass ratio plays an important role in the VIV response of the two cylinders. With increasing reduced velocity, both the upstream cylinder (UC) and downstream cylinder (DC) at m* = 3 exhibit the soft-lock-in phenomenon (at a lock-in frequency ratio of fy/fn < 1) instead of the typical lock-in phenomenon (at a lock-in frequency ratio of fy/fn ≈ 1). With increase in the mass ratio to m* = 10 and 20, the soft-lock-in phenomenon disappears, while the DC exhibits the typical lock-in phenomenon. The maximum amplitudes of the two cylinders notably decrease with increasing mass ratio. Furthermore, the mass ratio exerts a major impact on the distance between the two cylinders, which may change the flow pattern. The distance sharply decreases in the synchronization region at m* = 3 but remains almost constant at m* = 10 and 20. In addition, the wake mode and FSI mechanism are more diverse at a low mass ratio (m* = 3).