Study On The Characteristics Of Water And Sediment Movement In The Circular Arc Diffusion Type Forward Inlet Forebay Of A Pumping Station

Due to the unreasonable shape of the forward inlet forebay of large pumping stations,the flow field structure in the forebay is disrupted,resulting in serious sedimentation and reduced operational efficiency in the forward inlet forebay of pumping stations that draw water from muddy river flows.This study takes the forward inlet forebay of a typical pumping station in the Jingtaichuan Electric Power Irrigation Project as the research object,proposes a circular arc diffusion type pumping station forward inlet forebay shape,and uses theoretical analysis,numerical simulation,and on-site investigation methods to study the water and sediment movement characteristics in the circular arc diffusion type forward inlet forebay of a large pumping station.The distribution characteristics of the flow field structure,flow velocity,vortex structure,and sediment concentration in the pool are obtained,Revealing the impact of inward contraction of circular arc diffusion type side walls on the characteristics of water and sediment movement in the forward inflow forebay of pumping stations,exploring the sedimentation efficiency and mechanism of sediment in the circular arc diffusion type forward inflow forebay of pumping stations,and proposing effective measures to improve the flow pattern and prevent sediment deposition in the forward inflow forebay of multi sediment river water intake pumping stations.The aim is to provide reference for the design and renovation of similar pumping stations.The main conclusions are as follows:（1）A circular arc diffusion type forward inlet forebay shape is proposed to effectively improve the water flow structure in the forward inlet forebay of the pumping station.The single side wall of the forebay is composed of two circular arc shaped side walls.The first section of the circular arc is smoothly connected to the inlet channel of the forebay,controlling the diffusion degree of the forward inlet forebay along the water flow direction.The second section of the circular arc mainly serves to connect the first section of the circular arc and the side wall of the inlet forebay.When the pump station unit is fully open,the flow field structure in the forward inlet forebay of the arc diffusion type is basically symmetrically distributed,and the water flow diffusion effect is better than that of the straight diffusion type forward inlet forebay with a large diffusion angle.A mainstream area is formed in the center of the inlet forebay,a reflux area is formed on both sides,and vortices are generated in the reflux area;When the front pool side wall diffuses outward to a greater extent,the squeezing effect of the reflux zones on both sides on the mainstream zone is obvious;The inward contraction of the circular arc sidewall can effectively reduce the squeezing effect of the reflux zone on both sides,and the diffusion effect of the water entering the forebay increases significantly,reducing the scale of the reflux zone and vortex,reducing the reflux coefficient,improving the flow pattern of the water in the pool,and enhancing the stability of the flow field structure in the pool.（2）The flow velocity in the front pool of the pump station with circular arc diffusion type positive inflow is distributed along the vertical flow direction as high in the middle and low on both sides.There is a sudden decrease in flow velocity on both sides of the mainstream area of the inflow flow,which slightly rebounds near the side wall,and the mainstream effect in the central area is significant.The flow velocity in the mainstream area along the water flow direction gradually decreases along the process due to the diffusion effect of the water flow.As the degree of inward contraction of the arc increases,the flow velocity in the middle and surface mainstream areas of the forebay gradually decreases along the water flow direction,while the flow velocity in the bottom layer of the forebay gradually increases and the reflux intensity gradually decreases.However,when the degree of inward contraction of the circular arc sidewall is too large,the diffusion of water entering the pond is limited due to the small size and structure of the forebay itself.The circular arc diffusion type forward inlet forebay can effectively improve the uniformity of flow velocity distribution in the forebay and the cross-section of the suction pipe,and improve the inlet conditions of the water pump unit.（3）The distribution area of sediment concentration in the forward inlet forebay of the pump station is clearly divided.The low sediment concentration in the central area of the forebay is the low sediment concentration flow area,the backflow area on both sides is the high sediment concentration flow area,and the sediment deposition near the side walls on both sides is serious.The straight forward inlet with a large diffusion angle has a large area of high sediment concentration and high sediment deposition rate in the forebay.The flow passage of the forebay is compressed by sediment accumulation.The area of high sediment concentration in the forward inlet with a circular diffusion angle decreases with the increase of the inward contraction of the circular arc,while the area of low sediment concentration increases and sediment accumulation decreases.However,when the inward contraction of the circular arc sidewall is too large,the area of high sediment concentration increases,The accumulation of sediment has increased.The circular arc diffusion type forward inflow forebay can effectively enhance the sediment carrying capacity of the water flow,and the sediment deposition situation in the inflow forebay is improved.（4）The sediment concentration in the forward inflow forebay of the pump station is distributed in a vertical flow direction with a low concentration in the middle and a high concentration on both sides.There is a sudden increase in sediment concentration from the center to both sides.From top to bottom along the water depth,the sediment concentration in the pool and the scale of hyperconcentrated area gradually increase,the scale of hyperconcentrated area of surface flow is small,and the scale of hyperconcentrated area of bottom flow is large;At depths below 1.5m,the sediment concentration in the pool is greater than 1.06C₀,and the sediment concentration in the water body is relatively high.Sediment deposition is prone to occur within this interval.（5）The research results show that the arc Central angle of the side wall of the forward inlet forebay of the arc diffusion type.When the initial arc radius R₁ is between 2.91B and 2.56B,θat 44°to 52°,the water entering the pool diffuses more fully along the flow direction,with a good flow pattern and relatively improved sediment carrying capacity.This can effectively improve the sediment deposition in the forward inflow forebay of the muddy river water diversion pump station and improve the operational efficiency of the pump station.