Wake vortex regimes of a pitching cantilever plate in quiescent air and their correlation with mean flow generation

Abstract

Jet flows induced by oscillating cantilever plates enable power-efficient cooling enhancement and fluid acceleration. We report a combined experimental and numerical study of the vortex regimes present in the wake of a harmonically oscillating thin cantilever plate in a quiescent fluid and analyze their effect on the flow generation downstream. We use Particle Image Velocimetry (PIV) in conjunction with two-dimensional numerical simulations to investigate the vortex evolution around the trailing edge of the plates with different geometries and vibrational properties. Our observations suggest the existence of three distinct regimes in the wake: non-propagating, intermediate and propagating. Comparing the temporal decay of the vortex circulation in different regimes shows that different mechanisms are involved in the formation of these vortical patterns. A regime map is proposed next, denoting the incident of each vortex regime as a function of relevant dimensionless parameters. Our analysis of the mean jet on the normal mid-plane, as quantified by the momentum-averaged Reynolds number Rejet, shows that the induced jet downstream the trailing edge is tightly correlated with the identified vortex regimes. The present study improves our understanding of vortex generation and propagation in oscillating cantilevers and facilitates optimized design and operation of piezoelectric fans and similar devices.