Study of the effect of structural nonlinearities on rigid inverted flags using a cyber-physical experimental setup

Fluid-structural interactions between elastically mounted pitching plates and uniform flow commonly exhibit instabilities, large amplitude limit cycle oscillations (LCOs) and chaos within certain flow regimes. These phenomena are caused by the two-way coupling of unsteady aerodynamic loads and structural responses. Here, a cyber-physical experimental setup is used to explore aeroelastic phenomena beyond what is practical in traditional experiments. The setup consists of a rigid plate mounted on a torsional spring located at the plate’s trailing edge, in a rigid inverted flag configuration. Aerodynamic loads are imposed physically using a subsonic wind tunnel (Re ~100,000) and structural loads are imposed artificially using an electromechanical control loop.

The experiments are focused on introducing predefined nonlinear structural behaviors by way of the electromechanical control loop. We show that inverted flags with nonlinear restoring forces present variations in dynamic modes, oscillation trajectories, and the range of flow speeds for which flapping occurs. Outcomes from these studies will further our understanding of vortex-induced vibrations of rigid inverted flags and provide design guidance for system implementation as an energy harvester.