Research On The Dynamic Hydraulic Characteristics Of The Opening Gates Discharge Process On An Overflow Dam

In practice,subject to the influences of the reservoir operation instructions and nature runoff in watercourses,prevailing challenges such as the continuous change of gatage and weir head along with time are inevitable during opening gate discharge process in an overflow dam.However,current studies in the field of hydraulic engineering still adhere to the theories of steady state flow and model experiments as primary research methods.These situations not only restricted the significant development of hydraulic standards in China but also caused a number of engineering accidents owing to poor understanding of the discharge capacity and vertical vortex under transient conditions,leading to irrecoverable losses to lives and properties of the enterprises and people downstream.For above problems,this thesis developed a topology-alterative two-phase flow solver based on the self-adaptive offset dynamic layering method using the OpenFOAM platform and revealed the discharge capacity of an overflow dam and the flow mechanism of a vertical vortex by combining numerical simulations,prototype and model experiments.The main research achievements and conclusions of this thesis are as follows:1)Based on an overview of the related literature,the author has reviewed the orifice discharge formulae of a practical weir and the models of a free-surface vertical vortex from multiple aspects,such as theoretical hypotheses,application ranges,derivation of the governing equations and implementation of the model experiments.It is noticed that all the previously reported research methods have failed to take into account the transient influences onto the fluid field distribution with opening sluice gates.Considering the technologies of free-surface tracking and dynamic mesh in computational fluid dynamics,this thesis has established the dominating numerical methodology for simulating opening gates by combining the volume of fluid and the self-adaptive offset dynamic layering methods.2)The self-adaptive offset dynamic layering method which is a discretized simulation scheme of a plain or radial gate opening process is proposed by analyzing the movement characteristics of hydraulic sluice gates and introducing the self-adaptive offset matrix into the traditional dynamic layering method.Then,through the subsequent development of the topology-alterative two-phase flow solver,topoDyMFoam.the algorithm mentioned above is implanted successfully.Meanwhile,the working principle and process of topoDyMFoam are explained with an example.3)To verify the functional integrity and computational accuracy of topoDyMFoam.three confirmatory tests are further designed in this thesis.Both from qualitative and quantitative aspects,this thesis has examined the performance of the solver mentioned above in its temporary solution of the free-surface morphology,pressure,water level,discharge capacity.and water volume fraction on the premises of turbulent and parallel computing.The results demonstrate that topoDyMFoam not only realizes the opening process of the plain and radial gates but also shows excellent precision in simulating shock wave,surge before the gate,hydraulic jump behind the gate,hydraulic gradient vertical vortex,and other phenomena.4)With Shuanggou and Shilong reservoirs of the Songjiang River cascade hydropower stations as the research subjects,the author has designed two prototype experiments for addressing the opening radia]gates discharge process,By measuring the differences between the hydrostatic and total pressure heads at the monitoring points,the velocity components are obtained indirectly:and then the discharge capacity curves of the radial gates mentioned above are worked out based on the flow area controlled at the monitoring points.Furthermore,by introducing the correction coefficient of gate opening speed into the orifice discharge formulae of a practical weir,the discharge capacity curves of the two reservoirs are referenced under the normal and check flood water levels using the topoDyMFoam solver.5)With the opening gates discharge cases of the Pubugou,Shuanggou,Shilong reservoirs as the research subjects,the surface and underwater transient flow of each case are presented in detail with the free-surface,streamline,vorticity,velocity component,eigenvector,and the ?2 criterion vortex recognition algorithms.Based on this,the trigger,development,and decay mechanisms of the vertical vortexes are further explained.Among them,the trigger mechanism is the separation of flow under the joint effect of vortex flow on pier head and adverse pressure gradient in gate chamber when boundary conditions,angle of attack and Reynolds Number(Re)are appropriate;the development mechanism refers to the vortex deformation caused by expansion,shrinkage,shearing,and the vortex diffusion process under the control of the vorticity transport equation;and the decay mechanism is the dissipation of fluid kinetic energy under the control of enstrophy.