Vortex-induced vibration of a circular cylinder in the supercritical regime

Vortex-induced vibration (VIV) of a low mass ratio circular cylinder (m*=10), that is free to vibrate in crossflow and in-line directions, at supercritical Reynolds number (3×105) has been studied using large-eddy simulation for a range of reduced speed (2≤U*≤11). In the supercritical regime, the boundary layer transitions to a turbulent state via the formation of a laminar separation bubble (LSB). The regime is associated with weakened vortex shedding, resulting in subdued VIV response. Lock-in is observed for U*≥3. The cylinder vibration frequency is identical in the crossflow and in-line directions, leading to an elliptical trajectory. The rms of the force coefficients is similar to that for a stationary cylinder in the desynchronization regime while it decreases with increase in U* during lock-in. The spatiotemporal dynamics of LSB is explored. The LSB is sedentary in the desynchronization regime, while it undergoes significant circumferential movement, in each cycle of cylinder oscillation, in the lock-in regime. The mode of vortex shedding, determined from the arrangement of vortices in the span-averaged instantaneous flow as well as the phase difference between the lift and cylinder response, is C(2S) in the desynchronization regime. It is 2P0 in the lock- in regime.