Instabilities developing in the three-dimensional boundary layer on concave and convex curved surface

Abstract

The transition process on an infinite swept wing boundary layer subjected to both cross-flow and centrifugal instability is investigated experimentally. The model is a cylindrical wing with concave and convex profile segments. Detailed unsteady flow field measurements allow the analysis of the instability features and the description of the downstream disturbance development. On the concave segment, the quick growth of streamwise vortices gives rise to an early nonlinear development. In contrast to the transition process in the presence of pure cross-flow instability even at low free stream turbulence unsteady modes end up at very high amplitudes. The receptivity to free stream turbulence is increased whereas the receptivity to surface roughness is less pronounced. On the convex segment streamwise vortices are rather damped and the nonlinear development is changed.