The optimal spanwise effective angle of attack in flapping-wing propulsion

Abstract: The effects of the twisting-induced variation in the effective angle of attack, αe f f , on the aerodynamics and the leading edge vortex (LEV) of a flapping wing are investigated using the lattice Boltzmann method (LBM) and an immersed boundary method (IBM). If the wing is rigid during the flapping flight, αe f f of the outer portion of the wing would exceed a reasonable range. Wing deformation has been known to be able to improve flight efficiency, which adjusts αe f f along the wing span to maintain it within a reasonable range during flapping flight. In the simulations, the maximum αe f f at the wing tip is set from 9 to 54 in steps of 9 in this work. It is found that the wing achieves the highest propulsive efficiency by reallocating the force production in the streamwise and spanwise directions when the maximum αe f f at the wing tip is 27. Keywords: Flapping wing, propulsion, vortex dynamics