Flow-Induced Vibration and Energy-Harvesting Performance Analysis for Parallelized Two Flutter-Mills Considering Span-Wise Plate Deformation with Geometrical Nonlinearity and Three-Dimensional Flow

Abstract

Recently, micro wind energy harvesting devices such as flutter-mills have received considerable attention. The advantage of a flutter-mill over conventional wind power generators is that it can be easily parallelized. They increase the output power, but exhibit highly complex characteristics because the power generation performance depends on the distance and phase lag of vibration among the flapping sheets. This study reports the modeling and numerical simulations of the flow-induced vibration for two parallelized sheets under uniform flow, by considering the geometrical nonlinearity of sheets and wake shedding from the trailing edge. We modeled the fluid–structure and energy harvesting circuit interaction between two flapping sheets using the unsteady vortex lattice method for fluid and finite element method for the sheets, considering three-dimensional flow and span-wise deformation, to understand the complex interaction between two flapping sheets. The proposed model was verified by evaluating its performance against the results of computational fluid dynamics analyses and existing literature. Additionally, we examined the relationships between the aspect ratio of the sheets, harvested power, and phase lag between two flapping sheets using our model. Moreover, we confirmed the span-wise deformation to appear at a large inlet flow under a large aspect ratio, whereas the phase lag was confirmed to converge during the anti-phase mode when the flapping mode shifted to a higher level. In addition, we modeled the effect of the electrical load in a power generator circuit as the equivalent damping parameter of the sheets. Subsequently, we evaluated the optimal damping parameter of the sheets, which is equivalent to the electrical load in a power generator circuit, to obtain the energy from the fluid, and simultaneously, the phase difference of the flapping sheets converged to the anti-phase. In particular, when the distance between the two sheets is the same as the sheet length, the power generation performance is better than that of the single sheet.