Dynamics of Elastic Vortex Generators in Colony Configurations

Vortex generators (VGs) are widely used in engineering systems to promote mixing, enhance heat transfer, and control boundary layers. While rigid VGs are effective, they often incur significant pressure losses. Elastic vortex generators (EVGs), which passively deform in response to flow, offer a promising low drag/pressure drop alternative by adapting to unsteady fluid forces. Previous studies on single EVGs have identified three distinct dynamic modes: lodging, where the EVG bends and remains deflected; vortex-induced vibration (VIV), characterized by periodic oscillations and lock-in to the second natural frequency; and static reconfiguration, where mean deflection increases with stiffness and flow speed.

In tandem configurations, upstream–downstream interactions introduce additional complexities. Most notably, a distinct cavity oscillation mode arises in the downstream EVG due to unsteady suction and vortex trapping in the wake of the upstream element. This mode exhibits features akin to Rossiter-type flow instabilities, making it fundamentally different from the VIV behavior observed in isolation.

To further enhance mixing by EVGs, this work extends previous investigations of single and tandem EVGs to a colony of EVGs, inspired by the natural phenomenon of monami in submerged aquatic vegetation, where multiple elements interact not only with the incoming flow but also with large Kelvin–Helmholtz (KH) vortices propagating over the colony. Using high-fidelity two-way coupled fluid–structure interaction (FSI) simulations, we explore how collective dynamics evolve across different bending rigidity values and how element-scale instabilities and colony-scale KH structures jointly influence EVG behavior. Structural responses such as mean inclination angle, oscillation amplitude, and phase relationships are analyzed alongside flow field visualizations to identify dominant instability mechanisms.