Experimental Investigations of Vortex Occurrence at Transition in Unstable Laminar Boundary Layers

摘要

The behavior of laminar and instably stratified boundary layers towards three-dimensional perturbations, in form of vortices parallel to the direction of flow, was investigated by means of a water tunnel of very low turbulence. The theory of stability of such vortex perturbations in boundary layers may be of fundamental significance for the origin of turbulence. The artificially created vortex perturbations were photographically recorded by means of the tellurium method. For the first time it has been possible to verify the theoretically stated neutral curve of stability. Furthermore the distribution of the disturbation amplitude for different wave lengths and wall distances and also the growth of the vortices in the direction of flow were investigated. These experiments also give a verification of the theory of stability and show at the same time that the validity of the theory is limited to small disturbation amplitudes. (Author)