Growth and breakdown of streaky structures in boundary layer transition induced by free stream turbulence

Freestream turbulence is maybe the most important source to force by-pass transition in boundary layer flows. The present study aims at describing the initial growth of streamwise oriented disturbances in the boundary layer and relate this growth to recent theories of non-modal growth of such disturbances, but also to lay the ground for a predication model for free stream turbulence induced transition. It is shown that the initial growth is linear and proportional to the free stream turbulence energy. The spanwise scale of the disturbance does not change in the downstream direction and is probably determined by the scale of the free stream turbulence.