Low-Reynolds-Number Aerodynamics of a Flapping Rigid Flat Plate

摘要

Two- and three-dimensional low-aspect-ratio (AR = 4) hovering airfoil/wing aerodynamics at a low Reynolds number (Re = 100) are numerically investigated. Regarding fluid physics, in addition to the well-known leading-edge vortex and wake-capture mechanisms, a persistent jet, induced by the shed vortices in the wake during previous strokes, and tip vortices can significantly influence the lift and power performance. While in classical stationary wing theory the tip vortices are seen as wasted energy, here, they can interact with the leading-edge vortex to contribute to the lift generated without increasing the power requirements. Using surrogate modeling techniques, the two- and three-dimensional time-averaged aerodynamic forces were predicted well over a large range of kinematic motions when compared with the Navier-Stokes solutions. The combined effects of tip vortices, leading-edge vortex, and jet can be manipulated by the choice of kinematics to make a three-dimensional wing aerodynamically better or worse than an infinitely long wing. The environmental sensitivity during hovering for select kinematics is also examined. Different freestream strengths and orientations are imposed, with the impact on vortex generation and wake interaction investigated.