Numerical and experimental study on power extraction performance of a semi-active flapping airfoil with bioinspired dimple

Inspired from the special structure of dragonfly wings (cambered and corrugated groove), in this work, the bioinspired dimple structure is introduced into the design of the airfoil to improve the power extraction performance of a semi-active flapping airfoil, and the characteristic parameters of the bioinspired dimple structure are optimized by the combination of numerical analysis and Taguchi method. The results show that the bioinspired dimple can effectively improve the performance of the flapping airfoil. The average power coefficient and power extraction efficiency of the optimized dimple flapping airfoil are 31.73% and 31.23% higher than that of the baseline smooth airfoil respectively, and the influence of the three considered characteristic parameters on the power extraction performance is ranked as: lx (the location of bioinspired dimple) >ly (the depth of bioinspired dimple)>w (the inlet width of bioinspired dimple). Further analysis the flow field around the flapping airfoil shows that the bioinspired dimple can promote the separation of the leading edge vortex from the airfoil surface during stroke reversal, meanwhile at the process of upstroke and downstroke, the bioinspired dimple can also delay the leading edge vortex to separate, which is the reason for the dimple airfoil extract more power from the fluid. Based on the numerical results, experiments test are also carried out to evaluate the power extraction performance of the optimized bioinspired dimple airfoil, and the results show that at the same experiment condition, more 12.81% average power coefficient is extracted by the optimized dimple flapping airfoil, which again verifies the effectiveness of the numerical analysis conclusion obtained in this work.