Numerical Simulation Study On Hydraulic Characteristics Of Asymmetric Spillway Inlet

As is well known,the type and layout of spillway,one of the main outlet structures of the water control project,have a direct influence on the engineering safety.It is responsible for dredging and discharging,maintaining the safety and stability of the project.The spillway is usually placed on the shore or pass,and the favorable topography should be selected.The adverse effects of topographic structure,rock mass characteristics and hydrogeological factors on the flood discharge should be considered.Restricted by factors such as topography and geology,the topography of the entrance position is generally complex.In the discharge of flood,the flow direction of most projects is perpendicular to the entrance of open channel section.Considering the engineering characteristics,geological characteristics,construction environment and economic factors,the terrain conditions of some projects when spillway inlet section is installed are not ideal,the inlet section type is asymmetric,and the terrain is tortuous,resulting in the deflection of the incoming flow and the complex water flow form.The asymmetric inlet flow will lead to the disordered flow pattern at the inlet section of the spillway when the spillway is discharged,with the occurrence of complex vortexes and the unequal water depth between the two sides of the spillway,thus resulting in unstable spillway discharge capacity.Therefore,it is necessary to fully understand the complex geological form of the spillway inlet section,comprehensively consider the characteristics of topography,geology,excavation volume and so on,and reasonably optimize the spillway inlet section to ensure the stable and safe operation of the building.In the past,most of the researches on spillway were limited to the good condition of the inlet,but there were few studies on the unfavorable condition of the topography of the spillway inlet.Numerical selection and accurate simulation of spillway inlet is a difficult problem in computational fluid dynamics because of the problems of two-phase flow of water and gas and the collision between the fluid and buildings and fluids.Taking a water conservancy project as the research background,this paper conducts a numerical simulation study on a variety of layout schemes for the inlet section of the spillway under asymmetric flow.Key research methods and results are as follows:(1)By combining the CLSVOF method and RNG k~? model,this study aims to investigate the hydraulic characteristics of the spillway.Finite volume method was selected to discretize the governing equation,transient PISO algorithm was used to couple the pressure and velocity field,and non-structural grid was used to deal with the complex boundary of the computational domain.Numerical calculation was conducted for various operating conditions of the spillway.After analyzing the distribution of flow velocity and downstream water level in the inlet section,and through optimization,analysis and comparison,it is proposed to set two parallel guide walls of 20 m long and 13.6m high in the inlet section as the recommended optimization scheme.(2)The model test is used to determine the accuracy of the numerical simulation results.The test model is made according to the gravity similarity criterion with a scale of 1:40.The physical model test is conducted for the verification condition of the spillway.The overall and detailed flow patterns of the spillway under various operating conditions were observed experimentally,and the distribution of a series of hydraulic factors including the water level along the spillway,the velocity of the characteristic section,and the pressure on the weir surface were measured.The results show that the optimized model can effectively eliminate the inlet vortex,improve the adverse phenomena such as flow disturbance caused by asymmetric incoming flow,local water level obstruction and water wing formed on the side wall,and the overall hydraulic characteristics of the spillway meet the engineering requirements.(3)Comprehensively considering the influence of different numerical models on the operation results.The Standard k-epsilon model,RNG k-epsilon model and Realizable k-epsilon model were calculated and analyzed respectively with CLSVOF method.The accuracy of the numerical results was verified by the measured values of the experiment,and the coefficient of variation was introduced to calculate the fitting degree between the results and the test data.It is concluded that RNG k~? is the most suitable numerical model for the calculation of the flow conditions of the engineering.(4)The numerical model is applied to explore the optimal types of guide walls at the inlet of the spillway,and the improvement effect of different types of guide walls on the series of problems of severe whirlpool in the open channel section and the local water level of the spillway rising up is compared.Based on the comprehensive analysis of the topographic characteristics of the project site selection and the adjustment range of the optimization scheme,it is concluded that the optimal optimization range of the spillway inlet guide walls l is 15 ~ 20 m.This paper studies the hydraulic characteristics of the spillway under the adverse conditions of the inlet topography,which provides the technical support for the in-depth analysis of the complex flow field in the open channel section.