The velocity and vorticity fields of a single stream shear layer

Measurements of velocity and vorticity have been acquired in a large scale single stream shear layer. These data provided information regarding the nature of turbulent fluid flow at a relatively high Reynolds number. The Reynolds number dependence of phenomena is important given that many technological applications involve Reynolds numbers that are higher than those which are typically achieved in the laboratory. The use of the vorticity vector as an alternative variable to the velocity vector provides additional insight into the nature of these phenomena. Single and multi point measurements of both the velocity and vorticity have allowed the examination and comparison of the different scales of motion. The research project was effectively divided into two parts. The first involves the very near separation region in which a turbulent boundary layer separates at zero pressure gradient at a 90 degree edge. The measurements have shown the existence of a “sub-shear” layer. The vorticity that participates in the first instability is found to originate from the very near wall region. At larger y values, the separated turbulent boundary layer convects downstream adjacent to the sub-shear layer, “seemingly unaware” of the separation. The second part of the research involves measurements in the developed region of the shear layer. Several conclusions have been drawn from these data. For example, it has been shown that the dimensionless vorticity fluctuations do not scale in a self-similar way, but increase with Reynolds number. The cause of this is related to the large scale motions of the flow that lead to nonzero spatial correlations in vorticity over relatively large length scales.