Analysis of propulsive performance for dual flapping airfoils using CFD method

Dual flapping airfoils propulsion has many advantages than a single flapping airfoil, such as higher propulsive efficiency, easier mechanical design, more stationary lift and inertial force. The unsteady flow fields around flapping airfoils are simulated by solving Reynolds Averaged NavierStokes equations based on dynamically deformable hybrid grids. Some flapping parameters, such as plunging amplitude, plunging reduced frequency, spacing between the dual airfoils, phase difference between plunge and pitch of composite motion on thrust force coefficient, and propulsive efficiency, are studied by simulating the unsteady low speeds flow over dual flapping NACA0012 airfoils. It is found that dual flapping airfoils achieve a higher thrust force coefient and propulsive efficiency compared with a single flapping airfoil. It is also shown that there is an optimum phase angle of composite motion for a given flapping motion mode. The thrust force coefficient and propulsive efficiency of the composite motion are higher than those of the pure plunging motion.