Downstream of river intakes of hydro power plants, desilting chambers are usually provided in order to separate suspended solid particles from water, which cause abrasion at the hydraulic machinery. The sedimentation efficiency of a desilting chamber depends strongly on the three dimensional characteristics of the sand-laden water flow in the sand traps. Hence, the flow velocity in the chamber and its approaching channel, as well as the boundary shape of the transition from the approaching channel to the desilting chamber are found to be of high importance with regard to sedimentation efficiency. To investigate the 3D flow and turbulence filed in situ, field campaigns were performed in three different desilting chambers in the context of the present work. Acoustic Doppler Velocimeters (ADV) were used to measure the fluctuating three dimensional velocity components u, v, and w. An approach for the vertical turbulence intensity w'rms could be developed, being universally valid over the complete chamber length. Based on this non linear function, a new design formula has been developed to calculate the optimum chamber length of horizontal flow through desilting chambers.
Keywords: desilting chamber; settling efficiency; particle suspension; sediment transport; turbulence intensity; Acoustic Doppler Velocimeter
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