Genetic algorithm based optimisation of wing rotation in hover*

The pitching kinematics of an experimental hovering flapping wing set-up are optimised by means of a genetic algorithm. The pitching kinematics are parameterised with 7 degrees of freedom to allow for complex non-linear and non-harmonic pitching motions. Two optimisation objectives are considered: maximum stroke average efficiency and maximum stroke average lift. Solutions for both scenarios converge within less than 30 generations. The most efficient pitching motion is smoother and closer to a sinusoidal pitching motion, whereas the highest lift generating motion has sharper edges and is closer to a trapezoidal motion. In both solutions the rotation is advanced with respect to the sinusoidal stroke motion. The most efficient pitching motion is characterised by a nearly constant and relatively low effective angle of attack at the start of the half stroke. This supports the formation of a leading edge vortex close to the airfoil surface that remains bound for most of the half stroke. The highest lift generating motion has a larger effective angle of attack. This leads to the generation of a stronger leading edge vortex and higher lift coefficient than in the efficiency optimised case.