Flow Visualization in Free Shear Layers

This fundamental study is concerned in particular with the laminar-turbulent transition of the free shear layer in two-dimensional wall jets. Further detailed information of the vortex formations was provided by visualization in water using the hydrogen bubble technique. The observed vortex structures present in the shear layer during transition are dominated by transverse elements which grow exponentially as they are convected downstream in the flow direction. Longitudinal parts are also apparent given rise to an essentially three-dimensional nature of flow which develops soon in the shear layer. Further downstream the vortices break down three-dimensionally creating the onset of turbulence. An attempt was made to characterize the wall jet and its free shear layer in terms of the nondimensional Reynolds and Strouhal numbers.