Roughness effect on fully developed channel flow at low Reynolds numbers

Abstract

The effect of surface roughness arranged on one wall was investigated for a fully developed channel flow at low Reynolds numbers. The surface roughness was arranged with the roughness pitch ratio PR=2, 4 and 8. The friction coefficient was estimated from wall static pressure distribution. The streamwise mean velocity was measured with a particle image velocimetry. The Reynolds numbers were set in the range of R_eH ≅1000-6000, where R_eH is the Reynold number based on the channel height. The friction coefficient profile of PR=2 behaves like the transition from laminar to turbulent flows for R_eH <2000. The value of the friction coefficient increases with PR. For R_eH ≅1500, the value of the streamwise mean velocity profile of PR=2 is decreased near the channel center and increased near the walls compared to the parabolic profile of the laminar flow between parallel plates, but the profiles of PR=4 and 8 are decreased in the lower plate side with the surface roughness and increased in the upper plate side. For R_eH ≅2000, the velocity profile becomes nearly flat near the centerline of the channel for PR=2 and is almost similar to that of R_eH ≅1500 for PR=4 and 8.