Coupled Modal-Nonmodal Interactions Due to Periodic, Infinite Train of Convecting Vortices (TCV)

Events during transition to turbulence either follow modal or non-modal routes, or combinations of the two. Here, we report a computational investigation of strong freestream excitation caused by a train of convecting vortices. For this TCV excitation, we show a strong interaction of modal and non-modal components causing a spectacular growth of disturbances. We propose this as the mechanism for the severe encounters due to convective vortical disturbances on the underlying shear layer.