LAUSR

The power extraction performance of two semi-active flapping airfoils at biplane configuration is analyzed in this work through numerical approach. Two NACA0015 airfoils, which are regarded as an energy extraction turbine, are arranged in a biplane configuration to perform forced counter pitching motion and are subsequently induced in a plunging motion. A numerical code based on finite volume method to solve the Navier-Stokes equations coupled with finite center difference method to solve the passive plunging motion governing equation is developed to simulate the interaction between the two semi-active flapping airfoils and fluid. Results show that the semi-active flapping airfoil cannot absorb more power from the fluid with biplane arrangement, but this arrangement is beneficial for the power extraction efficiency of the airfoil. Analysis of the fluid field of the airfoil reveals that the wing-wing interaction can promote the vortex evolution and reduce the vortex magnitude of the suction side of the biplane airfoils with appropriate initial distance (hs = 2.5d). As a result, the maximum plunging of the biplane airfoils is smaller than that of the single airfoil. The smaller maximum plunging displacement contributes to the increase in power extraction efficiency.