Numerical Study of Flapping-Wing Flow Physics in Nonuniform Freestream Using the High-Order Spectral Difference Method on Dynamic Unstructured Grids

Abstract

In this paper, a numerical study is conducted to understand the impact of nonuniform freestream on the aerodynamic performance of a flapping foil. Specifically, an unsteady flow environment is generated by stationary inline or staggered circular cylinder arrays upstream. A 2D NACA0012 airfoil is then placed at different locations downstream of the cylinder arrays, and oscillates in the nonuniform freestream. Unsteady flows over the flapping foil are numerically simulated by solving the 2D low-Mach-number-preconditioned compressible Naiver-Stokes equations on deformable unstructured grids using the high-order spectral difference method. The flow fields over a pitching airfoil in unsteady flow environments and the corresponding aerodynamic forces are analyzed and compared under different flow conditions. It is observed that the nonuniform freestream can significantly affect the unsteady vortex dynamics of a flapping foil, thus modifying the thrust and lift generation.