Laser-Doppler-Anemometry measurements in a square channel with closely spaced ribs on a wall

The present study reports on results of Laser-Doppler-Anemometry (LDA) velocity measurements in a one-sided rib-roughened square channel with a rib-pitch-to-rib-height ratio of 3 and a rib blockage ratio of 6.7 % at a Reynolds number of 5.0 . 10(4). Distributions of the mean velocities, Reynolds stresses, and triple velocity correlations are presented. The results show the development of a three-dimensional secondary flow above the ribs resulting in a weakly advective wall-normal fluid transport between the near-rib flow and the channel core flow. However, the effect of the rib roughness on the turbulent flow and the accompanying turbulent exchange is limited to the immediate vicinity of the ribs. The rib induced unsteady flow processes and the diffusive transport, both derived from higher-order statistical moments, occur only in a narrow band above the ribs.