Transition Beneath Vortical Disturbances

Theory and computer simulations have led to advances in the fundamental understanding of how vortical disturbances induce transition in an underlying boundary layer. It is an intriguing process whereby the shear filters the disturbance, admitting only long streamwise wavelengths into the boundary layer. These develop into strong jets in the perturbation velocity field, which lift up into the upper portion of the layer. Then shorter wavelength perturbations trigger breakdown, ultimately producing a turbulent patch near the wall. Pertinent linear theory has evolved with time, but only with recent computer simulations has it been fitted into a picture of transition beneath vortical disturbances.