A Boundary Layer Transition Correlation for Concave Surfaces

Abstract

The boundary layer profile is observed to be highly distorted by the momentum transfer associated with Taylor-Gortler vortices. This distortion has the effect or increasing the boundary layer growth rate and modifying the start-or-transition momentum thickness Reynolds numbers from the flat plate value. For modest curvatures, the vortices carry turbulence towards the blade which promotes transition, but as the curvature is increased further, the boundary layer profile shape is stabilised and transition is delayed. A model for the distorted boundary layer is presented and is used to predict the boundary layer growth rate and correlate the start or transition results in terms of the momentum thickness and blade radius Reynolds numbers and the free stream turbulence level. The degree or profile distortion needs to be accounted for when predicting the end or transition.