Channel Flow Over a Smooth-to-Rough Surface Discontinuity With Zero Pressure Gradient

Abstract

Measurements are given for the combined effects of a change of surface roughness and a simultaneous change of pressure gradient. The latter is negative in a fully developed turbulent, two-dimensional smooth channel flow upstream of the discontinuity, but is artificially held to a value of zero in the rough channel following the surface discontinuity. Measurements of mean velocity, turbulent intensity, and wall shear stress in the current zero pressure gradient apparatus are compared with similar measurements made in the same apparatus with a negative pressure gradient in the rough channel. Results indicate that removal of the pressure gradient in the rough channel does not affect the growth rate of the internal boundary layer nor that of the sublayer; nor does the modified pressure gradient greatly reduce the transitional overshoot of wall shear stress and turbulence intensity previously observed.