Numerical Study of Two Flapping Airfoils in Tandem Configuration

The aerodynamics of two flapping airfoils in tandem configuration in forward flight was investigated numerically at a Reynolds number of 10 4 . The flow field was described by solving the incompressible Navier-Stokes equations. The flapping motion was handled with an overlapping moving grid method. The relationship between the phase angle and force production was studied over a range of Strouhal numbers and three different phase angles, 0, 90 and 180 degrees. Detailed comparisons were made with a single airfoil. In general, the lift, thrust and resultant force of the fore wing was increased compared to those of the single wing. The lift and resultant force of the hind wing was decreased, while the thrust was increased for the 0 phase hind wing and decreased for the 90 and 180 phase hind wings. The lift, thrust and resultant force of the combined fore and hind wings was also compared to the case of two isolated single wings. In general, the 0 phase case did not noticeably change the magnitude of the resultant force, but it inclined the resultant forward due to the decreased lift and increased thrust. The 90 and 180 phase cases significantly decreased the resultant force as well as the lift and thrust.