Fluid–structure interaction modes under complex unsteady vortices: a review

In complex unsteady wakes, the fluid–structure interaction (FSI) modes can differ significantly from those under uniform flows, often involving rich physical mechanisms. This paper reviews recent advances in three representative FSI phenomena: vortex-induced vibration (VIV) of cylinders, flapping of flexible plates, and locomotion of swimming/flying organisms. These phenomena are widely observed in both nature and engineering applications and span self-excited, active, and hybrid FSI modes. First, we compare the response modes under uniform and unsteady wake inflows. Results show that incoming vortices can substantially amplify vibration amplitudes of cylinders and plates, potentially triggering new instabilities. In contrast, biological swimmers may actively exploit incoming vortices by modulating their motions to enhance propulsion efficiency. Furthermore, this paper discusses potential applications of such FSI modes in complex wake flows, including enhanced energy harvesting from flow-induced vibrations and the development of bioinspired robots with improved sensing and decision-making capabilities. Finally, the challenges and future research directions in this area are outlined to guide further exploration.