Simulation of flow about flapping airfoils using finite element incompressible flow solver

A finite element how solver based on unstructured grids is employed for studying the unsteady flow past oscillating airfoils. The viscous how past a NACA0012 airfoil at various pitching frequencies is simulated. The variation of the force coefficient with reduced frequency is compared to experimental and other numerical studies. The effect of variation of the amplitude of the pitching motion on the force coefficient shows that the critical parameter for thrust generation is not the reduced frequency but the Strouhal number based on the maximum excursion of the trailing edge. The flow about the airfoil in a combined pitching and heaving motion, a mode found in many insects, is also simulated. The effects of varying the phase angle between the pitch and the heave motions is studied. The thrust coefficient was compared with experimental studies and good agreement is obtained. It is found that the maximum thrust coefficient is obtained for when the pitch motion leads the heave motion by 120 deg and maximum propulsive efficiency occurs at a phase angle of 90 deg.