Response of Fully Developed Pipe Flow to Rough Wall Disturbances (Turbulent Field)

Abstract

Hot-wire measurements were carried out in a fully developed turbulent pipe flow disturbed by rough wall sections (containing d- and k-type roughness) with emphasis being placed on the dependence of the statistical turbulence properties on the type of roughness. A sufficient length of pipe was provided downstream of the disturbance to ensure recovery to the equilibrium state. Noticeable differences between d- and k-type rough walls were found during the initial stage of recovery. In the case of k-type roughness, a considerable increase in the maximum turbulence intensity and velocity gradient was observed and momentum exchange violations were found to occur near the wall. For the d-type roughness, only a small variation in the velocity gradient appeared in the core region. No qualitative differences between d- and k-type flows were found for the intermediate and final recovery stages. The mean flow over the rough wall enhances the production of turbulence that depends on the type of roughness present. The rough wall produces an internal boundary layer which is found to eventually overwhelming turbulent diffusion in the recovery process.