Abstract
It is very important in Hydraulic Engineering to investigate the response of velocity distribution and wall shear stress to abrupt changes of wall roughness in closed channels as well as in open channels. We (1991, IAHR Congress) have first revealed the overshooting property of shear stress and turbulence in the case of smooth to rough changes in open-channel flows. In the present study accurate LDA measurements over abruptly changed roughness have been conducted in asymmetric closed-channel flows. Of particular significance is a very large overshooting of shear stress in the case of smooth to rough changes.It was also stressed that the eddy-viscosity model is not valid and a refined stress model should be developed for computation.
