Leading Edge Stall

Abstract

An airfoil is placed in a high Reynolds number but subsonic fluid flow and is subject to very slow perturbations of its angle of attack compared to the time scale of the flow. Asymptotic solutions for the Navier-Stokes equations are obtained for the boundary layer and interaction region flow structure on the airfoil. The viscous-inviscid interaction between the boundary layer and external inviscid flow is on a time scale sufficiently large such that the induced pressure gradient from the displacement of the boundary layer from the surface is negligible. Numerical solutions are found for the solvability condition from the method of matched asymptotic expansions, which ensures flow structure consistency. A short bubble of reversed recirculating flow forms on the surface of the airfoil. As time progresses, the angle of attack approaches a critical angle for a skin friction singularity and nonlinear breakdown. Discontinuous skin friction solutions are obtained for a second interactive stage equation. An eruption process from the bubble thickens the boundary layer and terminates the second interactive stage, resulting in a vortex, or eddy, spanning the boundary layer. The ejection of the vortex from the surface is the process of leading edge stall.

Date of Award	31 Dec 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jitesh Gajjar (Supervisor)