Boundary Shear in Circular Pipes Running Partially Full

The distribution of boundary shear stress in circular conduits flowing partially full, with and without a smooth flat bed simulating deposited sediments, has been examined experimentally ranging from 0.375 < F < 1.96 (F = Froude number) and 65,000 < R < 342,000 (R = hydraulic radius), using the Preston tube technique. The invert level of the flat bed and the water depth have been varied to simulate a wide range of possible flow conditions that may occur in culverts, sewers, and hydropower tunnels. The distribution of boundary shear stress around the wetted perimeter is shown to be highly sensitive to changes in cross-sectional shape. The results have been analyzed in terms of the variation of local/global shear stress versus perimetric distance, and the percentage of the total shear force acting on the wall or bed of the conduit. The %SFw results (%SFw = the percentage of the average wall shear force of the overall shear force) have been shown to agree well with Knight's empirical formula for prismatic channels. The influence of secondary flows on the distribution of boundary shear stress and the implications of this for sediment transport have also been examined.

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