Research On Hydraulic Characteristics And Optimization Measures Of The Forebay Of Fenghuangjing New Station

The forebay is a water intake structure,which has the function of leading the diversion canal to the inlet pool smoothly.Improper design and operation will cause problems such as sedimentation at the bottom,large-scale backflow and vortex in the pool.In the construction of the project,the forward inlet forebay is often used to ensure the flow pattern of the inlet water.The direction of the water flow in the forebay is the same as the direction of the drainage channel and the direction of the inlet pool.The diffusion angle has a direct impact on the flow pattern of the forebay.When the diffusion angle is large,the side wall will be peeled off.Backflow will worsen the water inlet conditions and threaten the safety of pumping station operation.Therefore,ensuring the uniform diffusion of the water flow in the forebay with a large diffusion angle provides an excellent water intake condition for the pumping station,which is of great significance to the stable and efficient operation of the pumping station.The Fenghuangjing New Station is a new pumping station planned to improve on the basis of the original Fenghuangjing Pumping Station project（hereinafter referred to as the old station）based on the original Fenghuangjing Pumping Station project（hereinafter referred to as the old station）in order to improve the water transfer guarantee rate of the water diversion project from the Yangtze River to the Huaihe River.Its forebay is a typical positive water inlet.Limited by the structural conditions,the diffusion angle of the forebay on the river diversion side is too large and the water flow conditions are complicated.Therefore,how to obtain the best flow pattern of the forebay on the river diversion side in the existing space is a key issue to ensure the safe and stable operation of the pumping station.In this paper,the research object is the forebay on the river diversion side of Fenghuangjing New Station,and the method of combining model test and numerical simulation is used to study the hydraulic characteristics of the water flow in the forebay.The main study contents are as follows:In order to study the hydraulic characteristics of the original designed pressure tank culvert water intake scheme,an overall normal model was built and the model test was carried out.The test results show that the existence of the transverse partition in the box culvert under the original design scheme causes the upper and lower layers of the water flow to not be connected.After the transverse partition is removed,there is a strong suction vortex on the side of the unit near the new station,which directly affects the water inlet conditions of the pump.When the water level changes,there is a problem of alternating open and full flow in the box culvert.There are many bubbles on the surface of the box culvert,which are squeezed and oscillated with the flow channel of the water flow,which endangers the safety of the building.In order to improve the many problems existing in the original design pressure tank culvert inlet,the design form of the open inlet forebay was proposed,and the calculation model was constructed using UG software.The RNG turbulence model and SIMPLIC algorithm were used to select the open inlet by FLUENT software.Numerical simulation calculation and optimization measures are carried out in the form of the forebay.Numerical calculation results indicate that:due to the thick original impeller layer of the old station,there is a dead water area at the junction of the old station and the fore pool,and the water flow is constantly tumbling;there are large-scale de-walled backflow vortices in the units on both sides of the fore pool,which penetrate from the surface layer to On the bottom floor,it spreads to the intake pool,affecting the normal inflow of the side units.In order to improve the unfavorable flow patterns in the open forebay,rectification optimization measures for adding bottom sills and columns are proposed.After comparative analysis,it is found that proper location and height of the bottom sill can effectively reduce the problem of off-wall reflux in the open forebay.The wall backflow problem can improve the uniformity of the flow rate of the inlet flow channel to a certain extent;the addition of multiple rows of uprights can also effectively reduce the scope of the backflow zone,but a single rectification method often has limited effect.The combined rectification method with a 1.2m high and 1.0m wide bottom sill and multiple combined uprights arranged behind the sill has the best rectification effect,and the flow rate uniformity has been significantly improved.On the basis of numerical simulation,a hydraulic model test of the open water inlet forebay was carried out,and the typical flow field and velocity distribution has carried on the contrast analysis,numerical simulation is verified the rationality of the optimized scheme and the calculation accuracy.The research results of the open inlet forebay in this article can provide improvement measures and suggestions for the design and construction of the Phoenix neck new station in the limited space.This has an important role in ensuring the safe and stable operation of the Phoenix neck pumping station,and it can also It provides a certain reference for the design and research of the forebay of similar pumping stations with large diffusion angles.