Study On Numerical Simulation Of Sediment Deposition In Forebay Of Pumping Station And It's Settlements In The Yellow River Irrigation District

The pumping station is the main building for the development of irrigation district,and the forebay is an important part of the pumping station,which can lead water flows smoothly into pump sump,providing good flow conditions for the pump.In the Yellow River irrigation district,there is sedimentation problem in forebays of most pumping stations because of the high sediment concentration of water source,affecting the normal and efficient operation of pumping stations.What leads to the sediment deposition in forebay of pumping station is not only the high sediment concentration of water source,but also the bad flow pattern.When water flows into forebay,there may be diversion,separation and some other bad flow patterns,causing whirlpool,reflux and low velocity zone in the forebay,and resulting in sediment deposition,which in turn intensifies the deterioration of flow pattern.Therefore,studying the flow pattern in forebay of pumping station and it's improvement measure is of great importance to reduce sediment deposition in forebay,and improve operation efficiency and economic benefits of pumping station.“Jingtaichuan Electrical Lifting Irrigation District in Gansu Province”(hereinafter called as “JingDian Irrigation District”(JID for short))is a Large Yellow River irrigation district located in the arid zone of northwest China.In this paper,the large pumping station in JID was taken as the study object,the sedimentation status in forebay of which was grasped through field investigation and survey,and the cause of sedimentation in forebay was primarily analyzed based on the basic theory.The forebay of pumping station with obvious and typical sedimentation was selected as the representation,and it's 3D model was built and unstructured meshed using ICEM-CFD.Then,the FLUENT was used to simulate and analyze the flow pattern in forebay based on the turbulence model of Standard k-?,exploring the mechanism of sediment deposition in forebay of pumping station,and through comparing the simulation results with the field investigation results,the rationality and reliability of numerical simulation was proved.For different forms of forebay,some optimization measures were proposed to prevent sediment deposition,and their implementation effects were analyzed by numerical simulation method.The main conclusions of this study are as follows:(1)In the Yellow River irrigation district,the front inflow forebay(Straight-edge and Curved-edge)of large pumping station has most serious problem of sediment deposition,in which the maximum deposition scope accounts for nearly half of it's volume;curved-edge front inflow forebay is an optimization of straight-edge front inflow forebay according to the deposition shape in straight-edge front inflow forebay,but the deposition problem in it is still serious;while the sediment deposition in side-direction forebay mainly distribute at the middle and posterior near outer wall,and it's degree is relatively weak.(2)Through the numerical simulation for different forms of forebay without optimization measures we can know that,the prominent sediment deposition in front inflow forebay is mainly caused by the serious main-flow effect.The flow in forebay has poor diffusion in horizontal and vertical direction,bringing about whirlpool,reflux and low velocity zone in the forebay,where the sediment carrying capacity of flow goes down;for side-direction forebay,the flow separates from the outer wall when arriving at the middle and forms low-speed reflux zone,where is easy to have a sediment deposition.The results of numerical simulation are consistent with the results of field investigation.(3)Sediment deposition prevention measures were proposed for front inflow forebays(Straight-edge and Curved-edge)and their implementation effect were analyzed with numerical simulation: for straight-edge front inflow forebay,the splayed diversion pier can't effectively improve the flow distribution in forebay,while the 45° pressure plate has significant optimization function;for curved-edge front inflow forebay,the 45° pressure plate also has obvious optimization effect,but the narrow water space at both ends of forebay weakens it's optimization effect in a certain extent.The study results will provide reference and basis for the renewal and optimizing design of pumping station in irrigation district and other similar pumping station projects.