Flapping Wing Energy Harvesting, Experiences with Modified Time Variations at high Re-Number

Abstract Wind energy converters with rotating blades are most common for energy harvesting. In special cases a system of flapping wings may be of interest where the wings are oscillating in combined flapping (plunging) and pitching modes respectively. Then the ratio of plunging and pitching amplitudes is of main concern: for animal flight the thrust production and its optimization as well as the sufficient lift force are important, for energy harvesting the maximum energy extraction from the oncoming flow and a minimized energy input into the system are of main importance. If one looks into the details of energy flows it is obvious that for animal flight the energy input via muscles is dominating whereas for energy harvesting main energy flow is transferred from the fluid into the oscillating system i.e., the direction of energy flow is reversed in both cases. With these fundamental aspects in mind, it is of interest to increase and optimize the energy input from the fluid. One important measure may be the modification of the time variation: usually the time varies harmonically within one period of oscillation. In the present paper modified time variations are investigated in detail. Phase variation between modes as well as dynamic deformation of the airfoil are of further concern and will be discussed in the present paper.