开机组合对泵站进水系统泥沙浓度分布的影响

Influences of start-up pump units on the sediment concentration for the intake system of a pumping station

针对泵站来流含沙条件下不同开机组合对进水系统泥沙浓度分布的影响问题,该研究开展了基于欧拉-欧拉算法的大型泵站进水系统固液两相流数值分析。首先,为了定量描述泥沙对流场均匀性的影响,对比分析了清水和浑水情况下进水流场的流速分布均匀度和回流系数,发现质量浓度10 kg/m^(3)且粒径为25μm的泥沙会使进水流场内的同轴漩涡变成沿水深方向更大尺度的螺旋状漩涡,进水池内的回流系数增长20.6%,流速分布均匀度下降8%。其次,通过对不同开机台数和机组组合方式下进水系统内泥沙浓度分布的对比分析,发现前池和进水池两侧边壁附近泥沙浓度最高,与引渠等宽的中心区域泥沙浓度最低,两侧边壁的泥沙浓度随开机台数的减少而增大,边机组不运行会破坏流场的对称性并在边机组与边壁区域形成死水区或漩涡区,增大泥沙浓度;基于开机组合的多工况分析,建立来流速度与流场内泥沙沉积效率的二次多项式模型。最后,开展了泥沙浓度与速度之间的相关性分析,发现泥沙浓度与横向速度平方呈幂函数关系,当泥沙粒径为25μm且质量浓度为10 kg/m^(3)时,进水流场的不淤速度为0.421 m/s,并且不淤速度随开机台数的减少而降低。研究结果可为含沙泵站进水系统防淤措施设计提供依据。

The uniform flow patterns of the pump intake system can dominate the efficient and stable operation of pumps.The for-bay,pump sump,and intake pipe are composed of the pump intake system in a pumping station.A large number of pumping stations in China are generally operated under the condition of sediment,particularly in the Yellow River Basin.The deposition of sediment in the pump intake system can deteriorate the flow uniformity during operation.The distribution of sediment concentration mainly affects the uniform pump intake flow,when the pumping station operates with the sediment inflow under the design water level.In this study,the Euler two-phase simulation was conducted to investigate the influences of the combination of start-up pumps on the sediment concentration distribution in the intake flow field of a large-scale pumping station.One kind of sediment particle size and one kind of sediment concentration were employed in the numerical simulations for a large-scale pumping station in Ningxia Hui Autonomous Region,China.Firstly,a comparative analysis of the single-phase and two-phase model was carried out to quantify the influences of sediment on the uniform intake velocity and the recirculation coefficient of the intake flow field.The presence of sediment affected the velocity distribution and vortex characteristics of the intake flow field in the pumping station.It was found that the recirculation coefficient of the pump intake system increased by 20.6%,whereas,the uniformity of the intake velocity decreased by 8% when the particle diameter was 25 μm and the sediment concentration was 10 kg/m^(3).Secondly,an investigation was made to clarify the influences of the number and position of start-up pump units on the sediment concentration.Another comparative analysis was performed on the design operating case with six pumps,two cases with five pumps,three cases with four pumps,and two cases with one pump.There was a high sediment concentration on the two sides of the fore-bay and pump sump and a low one in the central region.The sediment concentration on the two sides of the intake flow field increased,as the number of the start-up pump unit decreased.There were the severe negative effects of the unutilized side pump unit on the symmetry of the intake flow field,resulting in the dead water zone or vortices for the higher sediment concentration.A quadratic polynomial model of the start-up pumps and sediment deposition efficiency was established to determine the sediment concentration distribution in the multi-cases with different numbers and positions of start-up pump units.Finally,a correlation analysis was performed on the sediment concentration and transverse velocity.There was a power function correlation between the sediment concentration and the transverse velocity square at the bottom of the fore-bay and pump sump,even at the slice 0.2 m from the bottom of the pump sump.The trends of the sediment concentration and the transverse velocity were consistent in the direction of water depth.In multiple cases with a different number of start-up pump units,there were also the power function correlations between the sediment concentration and transverse velocity square,but the constant coefficients of the correlations were slightly different.The power function models indicated that the critical deposit velocity of the intake flow field was 0.421 m/s in the design operating condition when the particle size was 25 μm and the sediment concentration was 10 kg/m^(3).The critical deposit velocity decreased significantly,as the number of the start-up pump unit decreased.The achievements have theoretical significance and engineering applications for the high hydraulic performance of pumping stations.