Study On Shape Optimization And Sediment Deposition Response Of Forward Inflow Forebay In Yellow River Diversion Pump Station

In order to ensure the agricultural,production,living and ecological water use in Northwest China,optimize the use of water resources,and promote economic and social development,China has built a number of large-scale cascade irrigation projects in Northwest China.Pumping station is the most important hydraulic structure in large-scale cascade irrigation project,and its operation status is directly related to the water lifting efficiency,economic and ecological benefits of irrigation area.For the Yellow River Cascade irrigation project,due to the large sediment concentration of the Yellow River flow,the problem of sediment deposition in the forebay of the pumping station is very prominent,which seriously affects the normal operation of the project.Based on the numerical simulation method,this paper studies the hydraulic characteristics and sediment deposition characteristics of the straight-line diffusion type and curve diffusion type forward inflow forebay,discusses the sediment deposition mechanism,and puts forward the optimal shape parameters of the forward inflow forebay of the pump station.The main conclusions are as follows:(1)The velocity distribution of the forebay with different shape parameters is basically the same under all working conditions,showing the overall distribution trend of larger in the middle and smaller on both sides,larger in the surface and smaller in the bottom.However,due to the influence of the cross-section shape and bottom boundary of the approach channel,the diffusion effect of the flow at different depths in the same forebay is not consistent,The diffusion effect of surface flow is better than that of bottom flow.(2)For linear diffusion forebay,reducing the diffusion angle can effectively narrow the scope of backflow area and reduce sediment deposition,but too small diffusion angle will worsen the inflow conditions of pump units.In most operating conditions,when the diffusion angle is about 25 ° it can prevent sediment deposition and optimize the flow pattern in front of the water intake of the pump unit.(3)The start-up condition of the pump unit has a significant impact on the flow pattern in the forebay.Under the asymmetric start-up condition,the main flow will have obvious bias phenomenon.However,under the condition of small flow only concentrated in the middle unit of the pump house,due to the lack of lateral tension of the side unit,the plane diffusion effect of water flow is poor,even in the forebay with small diffusion angle,the phenomenon of sediment deposition still exists under this condition.For the condition that the flow is small and only the pump unit in the center of the pump room starts up,the water flow can not be fully diffused in the plane due to the disappearance of the lateral pulling force generated by the start-up of the side unit,resulting in a large range of backflow area.At present,all types of forebay can not effectively solve the problem of sedimentation,and the pumping station should avoid serious sedimentation caused by long-time operation in this condition.(4)Two kinds of optimized shape parameters of the forebay are proposed:The linear-curve combined diffusion forebay adopts the combined diffusion forebay with the combination of linear and curve boundary.The boundary of the forebay adopts the linear diffusion boundary with the diffusion angle ? = 20 ° and the length of 0.4 L / cos20 ° and the arc with the tangent radius R = 1.44 L.Hyperbolic diffusion forebay is composed of two arcs with unequal radius,the first arc radius R = 2.95 L,the center angle ? = 8.5 °,the second arc R = 2.19 L,the center angle ? = 16 °.