DNS of a Laminar Separation Bubble Affected by Free-Stream Disturbances

A series of direct numerical simulations of laminar, separating flow affected by various levels of free-stream disturbances has been performed. The free-stream disturbances were found to trigger a Kelvin-Helmholtz instability. The size of the separation bubble was found to be significantly reduced and the location of re-attachment was found to move upstream when the level of free-stream disturbances was increased. Downstream, the near-wall turbulent flow only very slowly assumes “normal” turbulent boundary layer statistics.