关键词: immersed boundary method, vortex street, aligned vortex, pitching airfoil, induced momentum

Abstract: The flow patterns and wake structures behind a pitching airfoil in an un-bounded domain have been studied extensively. In contrast, the flow phenomena associated with a pitching airfoil near a solid boundary have not been adequately studied or reported. This paper aims at filling this research gap by considering the flow confinement effects on the flow pattern around a pitching airfoil. To achieve this goal, the flow fields around a flapping airfoil in un-bounded, bounded and semi-bounded domains are studied and compared. Numerical simulations are carried out at a fixed Reynolds number, Re = 255, and at a fixed oscillation frequency corresponding to St = 0.22. An accurate immersed boundary method is employed to calculate the unsteady flow fields around the airfoil at various flapping amplitudes. It is argued that two flow mechanisms, here called “the interaction effect” and “the induced reverse flow effect” are responsible for the variations of the flow field due to the presence of a nearby solid boundary.

Key words: immersed boundary method, vortex street, aligned vortex, pitching airfoil, induced momentum