Flow-induced oscillations of a rigid inverted flag and their application to energy harvesting

The interaction between a flexible cantilever plate and a uniform flow that impinges on its free end is known to produce large amplitude limit cycle oscillations (LCOs) over a finite range of flow speeds. The above plate configuration is commonly referred to as an inverted flag or a cantilever plate in reverse axial flow and has potential applications in energy harvesting and vortex generation.

Here, a rigid inverted flag system is investigated composed of a rigid aluminum flag and a torsional spring that provides the restoring force required to exhibit large amplitude LCOs. This configuration is of interest because it is compatible with electromagnetic power generation and thus an efficient counterpart to systems utilizing piezoelectric components. The behavior of the system when subjected to a uniform flow is experimentally investigated in a subsonic wind tunnel. Flag kinematics and power output are measured, and system dynamics are studied as a function of several parameters including non-dimensional stiffness and flag aspect ratio.