Rough-wall turbulent channel flow is investigated via time-resolved tomographic particle image velocimetry (PIV). The optical refractive index of the transparent channel wall is matched with that of the liquid, allowing 3D measurements to be performed in the bulk flow as well as very close to the rough surface. The liquid is a concentrated solution of sodium iodide in water (62%–64% by weight). Roughness consists of staggered pyramidal elements that satisfy the “well-characterized” flow conditions. Our research is aimed at studying mechanisms involved generation of coherent structures as large-scale turbulence and the mean flow interact with the roughness elements, and their subsequent propagation away from the wall. We have adopted tomographic PIV to generate time-resolved, 3D data. Our measurements are performed at Reynolds number equal to 40000.

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