Unsteady aerodynamics of stationary/flapping airfoil combination in tandem

Unsteady flowfields over a stationary/flapping airfoil combination in tandem are computed using a Reynolds averaged Navier-Stokes solver. A single C-type grid is employed and the Happing motion of the trailing airfoil is implemented by deforming the grid in the near vicinity of the trailing airfoil. The unsteady effect of the flapping motion on the upstream airfoil is investigated by varying the location, the flapping amplitude and frequency of the trailing airfoil. Unsteady flowfields arc presented in terms of instantaneous vorticity contours, boundary layer profiles, unsteady and average pressure drag coefficients. It is observed that the flapping motion produces some drag reduction over the steady-state drag and some flow entrainment at the trailing edge for certain flapping amplitude and frequency motions. However, further numerical and experimental investigations are needed for better understanding of these complex unsteady interference effects