Low-Reynolds-Number Aerodynamics of Airfoils with Sharp Leading Edges

Abstract

The aerodynamic performance of conventional (rounded leading-edge) and reversed (sharp leading-edge) airfoils is investigated in the low Reynolds number regime. Computations are performed in the range Re ∈ [1x108, 8x104]. The results show significant differences in the flow structures and the aerodynamic characteristics of the two airfoil configurations. At Re ≤ 2 × 104, the reversed airfoil exhibits a higher lift coefficient in the entire range of angles of attack considered. This improvement is associated with a strong leading-edge suction peak produced by the formation of a leading-edge laminar separation bubble. The lift-to-drag ratio is also higher for the reversed airfoil in this Reynolds-number range. However, for Re ≥ 5 × 104, the conventional airfoil shows better lift behaviour. Flow-field analysis shows that the flow over the reversed airfoil separates at the sharp leading edge, transitions to turbulence, and subsequently reattaches to form a laminar separation bubble that enhances suction over a substantial portion of the upper surface. However, at higher Reynolds numbers, the laminar separation bubble is shortened, reducing its contribution to lift. A boundary-vorticity dynamics analysis further elucidates that the lift enhancement of the reversed airfoil at low Reynolds numbers is associated with a higher peak magnitude of the Lamb vector component ly in the separated shear layer close to the leading edge. However, at higher Reynolds numbers, the peak ly is located in the attached boundary layer of the conventional airfoil, leading to a higher lift coefficient. These findings provide key physical insights into the mechanisms governing the aerodynamic characteristics of sharp leading-edge airfoils at low Reynolds numbers.