Wake Signature and Strouhal Number Dependence of Finite-Span Flapping Wings

A numerical study was conducted in order to investigate the unsteady aerodynamics of finite-span flapping rigid wings. The unsteady laminar incompressible Navier-Stokes equations were solved on moving overlapping structured grids using a second-order accurate in space and time finite-difference scheme. Specifically, finite-span rigid wings undergoing pure heaving and root-flapping motions were studied. From the results presented, it is found that root-flapping wings produce wake structures similar to those of heaving wings, but with the difference that the latter wing kinematics generates larger vortices and forces than root-flapping wings; aside from this, similar wake regimes occur at comparable values of the Strouhal number. The numerical simulations were performed at a Reynolds number of Re = 250 and at different values of Strouhal number and reduced frequency.