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Mechanism of Secondary Currents Initiation and Maitanence in Open Channel Flows

Author(s): Shu-Qing Yang

Linked Author(s): Shuqing Yang

Keywords: Secondary currents; Sand ridges; Reynolds shear stress; Dip-phenomenon

Abstract: The mechanism for initiation and maintenance of secondary currents in open channel flows is investigated. This study first proves that the shear stress on an interface is caused by the timeaveraged product of streamwise velocity U and velocity V n normal to the interface, i.e., (-ρUV n), then the hypothesis that the turbulent energy is always transported to the nearest boundary for dissipation is introduced, finally the Reynolds equation is simplified and analyzed in the wall-normal and walltangent directions. This study reveals that the crucial role of solid boundary is the source of all turbulent eddies including the secondary currents; the wall-tangent gradient of streamwise velocity creates the secondary currents. In open channel flows, the sidewall, sediment strips and sand ridge/water depth result in the lateral variation of near-bed velocity, thus secondary currents appear in these flows. This theoretical finding is supported by experimental observations and the agreement between the predicted and measured secondary currents over sand ridge is acceptable.


Year: 2010

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