Instability Features Appearing on Swept Wing Configurations

In order to provide a more detailed physical understanding of transition on swept wing configurations possible instability mechanisms are studied in basic experiments. The models are chosen such that the individual mechanisms can be investigated separately as far as practicable. Most emphasis is placed on the identification of the sources of streamwise vortices which in many experiments on swept wings have been observed as dominant instability. In the stagnation region streamwise vortices only develop if a span-wise periodicity or a specific type of velocity fluctuations are superimposed upon the oncoming flow. In the unstable three-dimensional boundary layer, however, at turbulence levels < 0.15%, the streamwise vortices have proved to be the most amplified disturbance mode, contrary to the prediction of linear stability theory. In the three-dimensional boundary layer on a concave surface non-stationary waves are found as dominant instability.