Hydrodynamic visualizations of some turbulent flow structures

Flow-visualization techniques employing a transparent vertical hydrodynamic tunnel in conjunction with laser velocimetry have been used to investigate turbulent wakes behind two parallel cylinders and the structure of a turbulent boundary layer. Various modes of linkage between the wakes are identified and it is shown that if the rods are of different diameters, a counter-gradient turbulent stress appears in the central part of the wake. The observed phenomenon is attributed to coherent vortices. The structure of the turbulent boundary layer is found to be consistent with the accepted assumptions.