| The Yellow River Diversion to Qingdao Project is one of the key projects in Shandong Province during the seventh five-year plan period.Since its operation,it has achieved significant economic,environmental,and social benefits.It has effectively alleviated the pressure brought about by the uneven distribution of water resources in the Jiaodong Peninsula and provided valuable experience for the construction and management of long-distance inter-basin water transfer projects.However,due to the special characteristics of the Yellow River water system,such as high sediment content,the sediment accumulation problem in the front pool and the inlet channel of each pump station of the Yellow River Diversion to Qingdao Project is prominent,especially at the first pump station-Dayuzhang Pump Station.Therefore,conducting key technical research on anti-sedimentation for the Yellow River Diversion pump stations is of great significance to improve the operational efficiency and stability of the pump stations.With the support of the science and technology project of the Shandong Water Conservancy,entitled "Research and countermeasures on key technologies for preventing siltation in large-scale Yellow river water diversion pumping stations",this paper is based on numerical simulation technology of solid-liquid two-phase flow and hydraulic model experiments based on high-speed photography.Taking the Dayuzhang Pumping Station at the head of the Yellow River and Qing River Water Supply Engineering as the research object,the study sets a segmented forebay and baffle to investigate the main causes of sediment accumulation in the forebay and inlet channel of the Dayuzhang Pumping Station,as well as the effects of different anti-silt measures on the flow and sediment accumulation in the forebay and inlet channel.The main research content and results of this paper are as follows:(1)The particle size range of sediment particles in the Yellow River water system segment where the pump station is located was determined through sampling and analysis in the front pool and inlet channel of the Dayuzhang Pump Station.Based on this,the original Dayuzhang Pump Station was numerically simulated under the inflow conditions,and the main causes of sediment accumulation in the front pool and inlet channel of the Dayuzhang Pump Station were analyzed.The study found that the particle size range of sediment particles in the Yellow River water system segment where the pump station is located is 200-500 mesh,mainly concentrated in the range of 270-400 mesh;the original lateral front pool,the upper baffle near the front pool,and the diffusion section of the front pool all had large sediment accumulation.However,the reasons for the sediment accumulation at these locations were slightly different.The large sediment accumulation at the lateral front pool was directly related to the low-speed zone caused by the vortex,whereas the large sediment accumulation in the diffusion section of the front pool was related to the sudden expansion of the angle caused by the large expansion angle of the diffusion section,and the large sediment accumulation near the upper baffle was related to the fluid’s suction and the lateral diffusion of sediment in the front pool.(2)A segmented front pool was constructed by extending the baffle of the original Dayuzhang Pump Station and connecting it to the inlet channel.Based on this,the impact of different machine combinations on the flow state and sediment accumulation in the segmented front pool was studied through numerical simulation.The study found that under the segmented front pool scheme,the flow speed and flow speed distribution in the entire area were significantly improved compared to the original scheme,which is conducive to reducing the sediment accumulation,especially when all five pumps are running.When the flow demand is small and the full load conditions of the pump unit are not satisfied,it is necessary to prioritize the pumps located away from the lateral front pool to reduce the sediment accumulation in the front pool and inlet channel caused by the fluid’s suction in the lateral front pool location.(3)For the sediment accumulation problem caused by the sedimentation pool structure in the lower section of the front pool in the segmented front pool scheme,the effects of different installation methods of flow deflector plates on the flow distribution and sediment accumulation in the front pool and inlet channel were studied by installing flow deflector plates at the end of the lower section of the front pool.The study found that the installation of flow deflector plates can promote flow speed increase and reduce sediment accumulation at the bottom of the front pool through the flow-blocking effect.The flow-blocking effect increases with the increase of the installation angle of the flow deflector plate,while the flow deflector plate’s effectiveness decreases with the increase of the installation height.Therefore,to minimize the sediment accumulation in the lower section of the front pool,it is recommended to install the flow deflector plate with an installation angle of α=45° and an installation height of h/H=1/3.(4)By constructing a hydraulic model test platform and using high-speed photography technology,experiments were conducted to study the lowest starting flow velocity of sediment in the front pool,the flow velocity distribution law of characteristic sections near the lower section of the front pool under different operating conditions,and the effect of different installation methods of flow deflector plates on the hydraulic loss of the front pool.The study found that the lowest starting flow velocity of sediment in the front pool is about 0.15 m/s and is related to the small bottom vortex that appears near the bottom of the front pool.When only the segmented front pool scheme is used,due to the flow velocity of some measurement points near the bottom of the front pool section being less than 0.15 m/s,sediment accumulation is prone to occur,making it necessary to install flow deflector plates in the lower section of the front pool.When the installation angle of the flow deflector plate is α=45° and the installation height is h/H=1/3,the improvement effect of the flow deflector plate on sediment accumulation and the hydraulic loss caused can be effectively balanced.The research achievements of this paper have been successfully applied to the Dayuzhang Pump Station,the head pump station of the Yellow River Diversion to Qingdao Project.It has effectively improved the sediment accumulation phenomenon in the front pool and inlet channel,greatly enhanced the operational efficiency of the pump station,and received high praise from all walks of life.Moreover,it provides practical and feasible references for sedimentation control in large-scale pump stations in the Yellow River Basin... |
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