Influence of different inlet flow rates on pumping station sump vortex
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Abstract:
The bottom elevation of lower Yellow River main channel has been greatly reduced because of Xiaolangdi Reservoir several water and sand adjustments,resulting in a significant drop in the water level of the Yellow River,making the submerged depth of the horn nozzle of the pumping station into the pool that does not meet the pump requirements.The pump runs at an ultra-low water level,which causes deterioration in the flow pattern of the intake pool and changes in cavitation conditions,resulting in serious cavitation of the water inlet horn and pump impeller,unit vibration,and degradation of pump performance,etc.,which will force the unit in severe cases.The flow rate of the inlet water of the pumping station directly affects the flow pattern of the inlet pool of the pumping station.The turbulent flow pattern is often accompanied by the generation of vortices,which will not only reduce the performance of the pump but even cause the pump to cavitation,vibration,and unable to work. To explore the flow rate of the pumping station and the generation and development of the flow pattern and vortex of the pumping station′s intake pool,combined with the actual operation of the pumping station,the NX UG100 software is used to construct the drainage channel,fore pool,intake pool,and intake pipe.Taking pumping station water intakes physical model,and a three-dimensional turbulence mathematical model of the corresponding physical model is established.The calculation adopts the Reynolds NS equation,VOF model,and unsteady SSTk-ω turbulence model.The algorithm adopts the simple algorithm of flow field calculation.The discrete method adopts a limited volume method.The gradient adopts the least square method based on grid unit,the momentum,turbulent kinetic energy and turbulence dissipation rate adopt the second-order upwind style respectively.The inlet adopts the velocity inlet boundary condition,and the outlet adopts the velocity outlet boundary conditions,the water surface of the front pool and the inlet sluice chamber are set as the pressure outlet boundary conditions,and the atmospheric pressure reference point is selected as the contact point between the free water surface and the air.The rest are set as the wall boundary conditions,including: the front sump,the inlet sluice chamber,the side and bottom wall,the four walls of the inlet flow channel,the bell mouth and the outlet pipe wall are automatically processed by the SSTk-ωmodel until the flow difference between the inlet and outlet no longer changes or the water surface is stable,while the flow field is considered to reach in a stable state.9 different influent flow rates are selected,the characteristics of the influent water flow of the pumping station are numerically simulated,and the distribution of the influent flow field,the change of vortex,and the distribution law of the pumping station are analyzed under different influent flow rates. The research results show that when the inlet water velocity is between 0.322 2 m/s and 0.564 2 m/s,the intensity of the vortex on the surface of the pumping station increases with the increase of the inlet water velocity.When the inlet water velocity is 0.322 2 m/s~0.401 6 m/s,Type Ⅲ,and Ⅳ vortex appears in the inlet pool.Type Ⅴ vortex appears when the inflow velocity is 0.483 5 m/s,and Type Ⅵ vortex appears when the inflow velocity is 0.520 8 m/s~0.564 2 m/s. By comparing with the model test results,the two results are consistent.The research results can provide a reference for the engineering design of the pumping station.
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