Late stages of transition

Abstract

The region of non-linear disturbance activity is most important for understanding the physical processes which are responsible for the final transition to turbulence: in this area the perturbed flow becomes completely turbulent. Below we consider the prototypical mechanisms active both at the exponential growth of a single travelling two-dimensional linear instability wave, when it dominates in the flow, and at the predominance of stationary streamwise vortices generated by, for example, a surface roughness or crossflow instability. Mechanisms to explain the transition at high free-stream turbulence levels, with early formation of streaks are discussed in Chap. 5 and in separation bubbles in Chap. 6.