Numerical analysis of active chordwise flexibility on the performance of non-symmetrical flapping airfoils

This paper investigates the effect of active chordwise flexing on the lift, thrust and propulsive efficiency of three types of airfoils. The factors studied are the flexing center location, standard two-sided flexing as well as a type of single-sided flexing. The airfoils are simulated to flap with four configurations, and the effects of flexing under these configurations are investigated. Results show that flexing is not necessarily beneficial for the performance of the airfoils. However, with the correct parameters, efficiency is as high as 0.76 by placing the flexing centre at the trailing edge. The average thrust coefficient is more than twice as high, from 1.63 to 3.57 with flapping and flexing under the right conditions. Moreover, the single-sided flexing also gives an average lift coefficient as high as 4.61 for the S1020 airfoil. The shape of the airfoil does alter the effect of flexing too. Deviating the flexing phase angle away from 90° does not give a significant improvement to the airfoil’s performance. These results greatly enhance the design of a better performing ornithopter wing.