Velocity measurements of a free-surface turbulent flow over smooth and rough beds


Abstract: The effect of different types of surface roughness on a turbulent boundary layer was studied using 1D velocity measurements in a relatively high Reynolds flow. The roughness consisted of trapezoidal ribs with horizontal spacing and roughness height $k$. The roughness elements were aligned in a direction transverse to the flow. A series of 7 tests of fully rough turbulent subcritical flow over two-dimensional transverse repeated trapezoidal ribs was undertaken, in which the ribs were varied to give uniform rib spacing-to-height ratios of p/k = 6--36. Measurements of the velocity were carried out over a range of Reynolds numbers, 81735 $<$ Re $<$ 144,110. The results show that the mean profiles of all the surfaces collapse well in the velocity defect form.

Keywords: Roughness function $\Delta U^{+}$, trapezoidal rib roughness, turbulence, velocity profile

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