Shear Layers Bounding Separated Regions

Abstract

Experimental mean velocity and turbulence data obtained within two rather different separated flows are presented and discussed. Attention is concentrated on the nature of the thin wall boundary layer developing beneath the separated regions and on the differences between the two separated shear layers and plane mixing layers. It is shown that the shear layers are not only rather different from one another — largely because of the difference in the nature of the separation in the two cases — but also differ from a plane mixing layer in a number of ways. Turbulence stresses are significantly larger than they are in the plane mixing layer; it is shown that whilst in one case their behaviour may be dominated by the effect of the wall coupled with entrainment of turbulent fluid returned around reattachment, in the other case mean flow curvature effects are much more significant. Despite these differences the data indicate that the nature of the wall boundary layer may be rather less dependent on flow geometry. It seems that the mean velocity profile in this boundary layer can be described as a function only of the wall friction, the location and value of the maximum (negative) velocity and the pressure gradient.