Abstract
The unperturbed flow configuration is almost the same as that used by Hanjalic & Launder, and as in the fully developed asymmetric flow region, the positions of zero velocity gradient and zero Reynolds stress do not coincide along the whole course of the relaxation process. One of the most striking features of this flow is that in the internal layer formed downstream of the step change in roughness, Prandtl's mixing length increases considerably over the value given by the relation l=xy. Correspondingly, the so-called universal constant A, in the law of the wall, decreases significantly in this region, where the convection term in the turbulent energy equation is found to play an important role and the flow is far from the equilibrim condition.
