泵站正向进水前池扩散角对池内流场结构的影响

Influence of diffusion angle on flow field structure in forward intake forebay of pumping station

针对从多沙河流取水的大型泵站进水前池内水流流态较差,易在池内产生大尺度回流区域,导致泥沙严重淤积等问题,该研究以甘肃省景泰川电力提灌工程典型泵站的正向进水前池为研究对象,构建不同扩散角体型结构的正向进水前池三维模型,基于Mixture多相流模型和Realizable k-ε模型开展数值模拟计算,阐明了正向进水前池流场结构特征,提出了有效改善正向进水前池流场结构的扩散角范围。结果表明:泵站机组全开时,正向进水前池内流场结构对称分布,在进水前池中央形成主流区,两侧形成回流区,中央主流区域水流流速远大于两侧回流区,主流效应显著;随着扩散角的减小,两侧低流速区面积减小,主流区域流速呈下降的趋势,区域宽度呈现增加的趋势,进入前池的水流扩散效应增加明显;扩散角在25°~30°之间时,入池的水流沿流程发展和扩散较为充分,有效改善多泥沙河流引水泵站前池的泥沙淤积,研究成果可为同类泵站的设计和更新改造提供指导和参考。

A pumping station is widely used in a water distribution system for the efficient and reliable transportation.However,the sediment deposition can pose an outstanding decrease in the operating efficiency of pump station.Particularly,the water is taken from the river with the high content of sand,such as in the Yellow River Basin.More importantly,the low flow pattern and large-scale backflow area can often occur in the forward intake forebay of a large-scale pumping station.The current anti-siltation measures cannot effectively improve the intake field structure in large-scale pumping station,due to the multiple dimensions,and single rectification.In this study,a systematic investigation was made to clarify the influence of diffusion angle on the flow field structure in the forward intake forebay of a pumping station.The typical research object was taken as the forward intake forebay of large-scale pumping station in Jingtaichuan Electric Power Irrigation Project in Gansu Province of China.A field investigation was firstly performed on the sediment deposition in the forward intake forebay of pumping station.The sampling was then implemented to analyzed the variation characteristics of sediment concentration and sediment particle size in the water flow from pumping station.A three-dimensional model was also established for the forward intake forebay with the different diffusion angle.Numerical simulation was carried out using the Mixture multiphase,and Realizable k-εmodel.The actual flow measurement was utilized to verify the accuracy of the numerical calculation.The characteristics of flow field structure were clarified in the forward intake forebay,together with the variation under the diffusion angle of the forebay.The mechanism of sediment deposition was revealed to propose the diffusion angle range for the optimal flow field structure in the forward intake forebay.The results show that the flow field structure was symmetrically distributed in the forward intake forebay of pumping station under the design operation conditions of the unit.The mainstream area was formed in the center of the intake forebay,whereas,the backflow area was formed on both sides.The flow velocity and the ability of current to carry sediment in the central mainstream area were much higher and stronger than those in the backflow area on both sides.The sediment deposition decreased significantly from the both sides to the center,indicating the significant mainstream effect.Furthermore,the squeezing effect of vortices was weakened in the backflow areas on both sides of the intake forebay on the mainstream area,as the diffusion angle of forebay decreased,while the area of low flow velocity on both sides also decreased significantly.At the same time,there was an increasing trend in the width of the central mainstream area,whereas,a downward trend was found in the flow velocity in the mainstream area.The ability of current to carry sediment increased to promote the performance of the flow diffusion entering the forebay.Once the diffusion angle was between 25°and 30°,the flow entering the pool was well developed to diffuse sufficiently along the pipeline,indicating the better flow pattern with the much more stable structure of flow field.The sediment deposition was effectively reduced in the forebay of the diversion pumping station on the sandy river.As such,the operating efficiency of pumping units was improved to guarantee the realistic benefit of irrigation project.The research findings can also provide the strong reference to design and update the large-scale pumping stations.