Optimal Mechanical Properties for Energy Extraction from Plates Subjected to Discrete Vortex Loading*

The optimization of energy extraction from coherent vortical structures using flexible membranes is a subject of interest in recent work. The focus of this study is to find the optimal properties of a plate that, when subjected to a discrete vortex passing tangentially over it, maximizes the plate strain energy. Vortex rings are generated with Re≈4300 and the vortex to plate spacing is varied. The plate mechanical properties are expressed in terms of a non-dimensional mass parameter (Π_m), and a Strouhal number (St), where the St number expresses the duration of pressure loading relative to the period of plate oscillation. It is hypothesized that a St≈0.5 will optimize the fluid to plate energy transfer. Four sets of plates with mass parameters that span the range of 3<Π_m<11 are investigated for Strouhal numbers that span the range of 0.2<St<1.0. It is observed that the energy transfer is optimized for St≈0.5, and that this value is largely insensitive to the plate mass parameter and vortex/plate separation distance. The results are applicable to predictive energy harvesting design efforts.