Theoretical Study of Leading-Edge Bubbles and Leading-Edge Stall of Airfoils

The small separation bubbles which form near the leading edge of airfoils prior to the onset of leading-edge stall have been analyzed in detail, including the effects of viscous-inviscid interaction. The separated laminar shear layer, transitional flow and turbulent reattaching flow are represented by an integral formulation. A correlation of local shear-layer parameters has been developed for determining the onset of transition in the laminar shear layer. Solutions are obtained using an iterative procedure, with strong interaction effects limited to the immediate vicinity of the separation bubble. Results obtained for specific airfoils are in good agreement with wind tunnel measurements. The method was used to investigate the mechanism for bubble bursting. Results indicate that reseparation of the turbulent boundary layer downstream of reattachment, rather than failure of the shear layer to reattach, causes bubble breakdown. (Author)