Flow physics of bioinspired passive multi-flap wings with variable stiffness

Covert feathers on the suction side of a bird's wing are observed to flap passively during high-angle-of-attack maneuvers. This observation inspired the incorporation of bioinspired flaps to the suction side of aerial vehicles to improve flight performance at high angles of attack. Prior experimental and computational research by the author and others investigated the effect of varying the number and chord-wise position for multi-flap systems and the variation of the flap's hinge torsional stiffness in single-flap systems. However, the impact of torsional stiffness on multi-flap systems has not been studied. In this work, we use time-resolved force and flowfield measurements to systematically study the impact of torsional stiffness in multi-flap wings on the aerodynamic performance and the flow physics of an airfoil at Reynolds number Re=200,000. In addition, we quantify the deflection dynamics of each flap and study the interplay between their motion and the coherent unsteady flow structures in the flow.