The spatial inhomogeneity of turbulence over large relative random roughnesses in open channel flow

Turbulent boundary layers over roughness elements have considerable engineering interest in several disciplines, e. g., mechanical, aerospace, environmental and hydraulic engineering. In the work presented attention was focused on turbulence characteristics over relatively large random roughness. The measurements were obtained with three component acoustic Doppler (ADV) and two component laser Doppler (LDA) velocimeters. The turbulence statistics associated with the vertical velocity component are emphasized including mean vertical velocities, root mean square (RMS) distributions and mean vertical momentum fluxes. The process of flow rush into the hole between roughness elements is investigated. It was found that the vortices, which form in the holes between the roughnesses are key to the process. Flow visualization observations and data analysis are a sign of the vortices entrained through the hole at the downstream side and sucked out from hole through at the upstream side by the main flow.