Numerical study of tandem flapping wing aerodynamics in both two and three dimensions

In this paper we extend our previous two-dimensional tandem wing study to three-dimensions. In our previous study we found that vortex interactions highly depend on the phase lag angle and spacing between the forewing and hindwing. In this paper the effect of phase lag angle between the fore and hind wings on the wing-wing interactions, force production, and efficiency of the hindwing was studied for three different phase lag angles, 0°, 90° and 180°. The spacing used between the forewing and hindwing was one chord. A single frequency sinusoidal pitch-plunge motion was used at a Strouhal number of 0.3 and a Reynolds number of 200. The aspect ratio of the three dimensional wing was two. The simulations were based on the incompressible Navier-Stokes equations, discretized on overlapping grids. The wing motions were prescribed by a series of composed transformation matrices. A moving overlapping grid technique will be used to handle the moving boundary problems. It was found that the three dimensional cases exhibited a spanwise variation in the LEV structure and a weaker LEV formation at midspan compared to the two-dimensional cases with the same kinematics. The spanwise variation resulted in weaker vortex interactions between the fore and hind wing than predicted by the two dimensional study.