Numerical Investigation of Low-Aspect-Ratio Wings at Low Reynolds Numbers

Abstract

A numerical analysis is performed to study the flow around low-aspect-ratio (LAR) wings and more particularly the resulting lift-and-drag force. The research is focused on low-Reynolds-number aerodynamics, as LAR wings are crucial for the development of microair vehicles (MAVs). The flow around LAR wings is characterized by complex three-dimensional flow phenomena. These phenomena include wing-tip vortices, flow separation and reattachment, laminar to turbulent transition, and a mutual interaction among these phenomena. The flow is studied using a commercial computational fluid dynamics (CFD) program and a strip method. The CFD code is used to investigate the three-dimensional flow aerodynamics of rectangular LAR wings with an aspect ratio between 0.5 and 2 at a Reynolds number of 1 x 10 5 . Simulations on a flat plate and a reflex-type low-Reynolds-number profile (S5010), which is representative for a flying-wing MAV, are performed and compared. Experimental data is used for comparison and validation. The effects of flow separation and low Reynolds numbers are further investigated using a strip method. Two accurate formalized methods to predict lift and drag are derived. The first method is applicable to profiled wings with moderate low-Reynolds-number effects. The second method, which is based on the strip method, is more general and is also applicable to flat plates and wings exhibiting large regions of flow separation.