On the wake-induced galloping of one-fixed-one-free tandem cylinders at subcritical Reynolds numbers

To investigate the characteristics of the wake-induced galloping (WIG) phenomenon at subcritical Reynolds numbers, large eddy simulation (LES) is adopted to simulate the cross-flow around one-fixed-one-free tandem cylinders at Re = 3900 and 15 000. The WIG phenomenon is numerically reproduced when the downstream cylinder (DC) has single- or two-degree-of-freedom (2DOF), and is verified against the existing experimental data. The research reveals that the wake regime is the 2T mode, consistent with the superupper branch of the 2DOF vortex-induced vibration of a single cylinder. The WIG mechanism is attributed to the coupling between the cylinder oscillation and the upstream-shed vortices. The DC's oscillation offers space for the growth of the opposite-side vortices, enabling them to fully develop before reaching the DC. Subsequently, the interaction between the vortex structure and the side of the DC leads to surface pressure variations, propelling the cylinder to move in the opposite direction and establishing a stable galloping frequency and amplitude. Analysis also indicates that the galloping response is governed by the upstream cylinder's vortex shedding frequency and the wake regime, which is closely associated with the Reynolds number and inflow conditions.