Influence of the aspect ratio of the sheet for an electric generator utilizing the rotation of a flapping sheet

The “Flutter-mill” is a power generation device that can be parallelized and downsized more easily than conventional wind-power generators with the added advantage of lower manufacturing costs. Flutter-mills comprise a flexible sheet with an electric power generator at its leading edge. Flutter-mills exhibit complex power generation performance characteristics that are highly dependent on the specifications of the flexible sheet and the inlet flow velocity. In particular, the span width of the sheet affects the stability and flapping behavior significantly. Using the numerical analysis model, these complex flutter-mill characteristics can be estimated without experiments, and thereby numerical model inform the choice of the sheet dimensions, which are critical for designing an effective flutter-mill. Here, we present a numerical model that can provide a preliminary survey of the power generation performance and attempt to clarify the relationship between the aspect ratio of the sheet and the harvested power. The equation of motion for a flexible sheet includes rotational damping at the leading edge of the sheet to emulate the coupling effect between the sheet and the energy harvesting circuit. We verified the validity of our numerical model by evaluating its performance against previously published experimental results, and thus established the relationship between the aspect ratio of the sheet and the harvested power. We found that the local minimum value of the harvested power of the flutter-mill may be caused by the vibration amplitude at the leading edge of the sheet decreasing in the transition domain of the flapping vibration mode if the aspect ratio is large.