Numerical Investigation Of The Flapping Foil Based Energy Harvesting System

As renewable energy,wind and tidal power have the advantage of wide source,free from contamination,and have become the field that people concerned very much.Be capable of extracting energy from free flow and output electric energy through generator,the flapping foil based energy extraction system has attracted the attention of scholars as a kind of biological simulation device.Compared to the traditional turbine with horizontal axis,the tip speed of the flapping energy harvesting system is small,thus the system is environmentally friendly due to the reduced aerodynamic noise.Although there have been a number of experimental and numerical investigations about the influence of different motion parameters of a flapping foil on its performance,but they all assume that the incoming flow is uniform and steady,very few studies have been focused on the influence of the instantaneity of the incoming flow.But in real flow field,the flow is often non-uniform and plays an important role on the performance of the flapping foil.The two-dimensional fully activated flapping foil based energy harvesting system in the gust flow is investigated in this work.By changing the frequency and strength of the gust,the phase difference between the gust and the flapping motion,the energy extraction efficiency is obtained.After the analysis of the laminar flow at Re=1100 and the turbulence flow at Re=5×10~5,it's found that the frequency of the gust has little effect on the efficiency of the system,while the strength of the gust and the phase difference between the gust and the flapping motion of the foil play great role on it.Next,the semi-activated flapping foil based energy capture system is also studied in this work.The pitching motion of the foil is the prescribed cosine function while the heaving motion is stimulated by the periodic lift force on the foil.When the flow is uniform,the optimization of dimensionless damping constant is confirmed at k*=5,the optimization of dimensionless spring constant is set as b*=? when ?_m?67.5° and b*=0.5? when ?_m?67.5°.After confirming the optimization of the spring and damping constants,some similar conclusions compared to the fully activated flapping foil are drawn after the analysis of the gust strength and phase difference on the performance of system.