The Effect of Large Free Stream Disturbances on the Stability of Two- and Three-Dimensional Stagnation Flow

Kurzfassung

One of the most crucial problems in transition research are two- and three-dimensional stagnation flows. In wind tunnel experiments numerous evidence has been found for the formation of streamwise vortices around attachment lines. These streamwise vortices distort the subsequent boundary-layer flow and change sthe stability characteristics of the velocity profiles so that transition is affected. In the past the appearance of streamwise vortices was attributed to centrifugal instability but recent analyses which assume exponentially decaying disturbances proved stagnation flow to be stable with resspect to centrifugal instability. Hence, the question arises what other instability mechanism could lead to the streamwise vortices observed. H. Ludwieg 1 suggested that large scale velocity fluctuations in the oncoming flow as appearing in turbomachinary e.g. could lead to such an instability.