Secondary instability and transition in three-dimensional boundary layers

Abstract

In the highly accelerated three-dimensional flow near the leading edge of a swept wing stationary and travelling crossflow modes are the most prominent disturbances. Near transition onset secondary three-dimensional instabilities of high frequency can be observed in such flows. A model flow on the basis of a DLR swept plate experiment allows a detailed study of transition scenarios triggered by crossflow instabilities, since the favourable pressure gradient over the whole plate inhibits instabilities of Tollmien-Schlichting type. In order to shed some light upon the role of the high-frequency secondary instabilities, the saturation characteristics of crossflow vortices in this model flow are investigated using the parabolised stability equations [1]. In contrast to nonlinear equilibrium solutions [3] of steady crossflow vortices, the PSE results yield different maximal disturbance amplitudes for different initial amplitudes