Numerical Simulation Analysis Of Transient Flow In Viscoelastic Water Conveyance Pipeline

The water pipeline is an important part of the urban water supply system,and its operational status will have a major impact on the safety of water supply and the water transmission capacity of the pipeline network.At present,the research on the prevention and control of the damage caused by the transient flow in the water pipeline mainly focuses on the elastic pipeline.However,with the development of polymer materials technology,viscoelastic pipes are widely used in China.In order to accurately understand the actual pressure fluctuations in viscoelastic pipes,transient flow models for viscoelastic pipes are established and the influences of different factors on the simulation accuracy of pure liquid phase and gas-liquid two-phase transient flow are analyzed.Firstly,the problem of pure liquid transient flow in viscoelastic pipe is simplified,and the basic differential equation is deduced in detail.Assuming that the friction coefficient does not change,a pure liquid transient flow model of viscoelastic pipe is established.According to the experimental results in the literature,the accuracy of the transient flow model for the viscoelastic pipeline and the transient flow model for the elastic pipeline under different flow conditi ons is compared.The results show that considering the viscoelasticity of the pipeline,the accuracy of the pure liquid transient flow model can be significantly improved,and the maximum relative error of the amplitude of the pressure wave can be reduced to 0.37%~6.34%.The smaller the wall constraint coefficient,the larger the amplitude of the pressure fluctuation obtained.Then,the friction model of viscoelastic pipe is modified,and the improved IAB friction model and Vardy-Brown friction model are introduced respectively.The transient models of viscoelastic pipe-only liquid-phase transient flow with transient friction models are established.According to the experimental results in the literature,the accuracy of simulation of pure liquid transient flow model in high-density polyethylene pipes and medium-density polyethylene pipes in different flow states is compared.The results show that the modified friction model can improve the accuracy of the pure liquid transient flow model.When the Vardy-Brown friction model is introduced,the simulation results are closer to the experimental results.The maximum relative error of the amplitude of the pressure wave is 0.22%~4.46%.Finally,the gas-liquid two-phase transient flow in viscoelastic pipelines is studied.Different friction models are introduced to establish a transient model of gas-liquid two-phase flow in a viscoelastic pipeline.According to the experimental results in the literature,the accuracy of the simulation of the gas-liquid two-phase transient flow models for viscoelastic pipes with different friction models under turbulent flow conditions are compared.The conclusions are as follows: for viscoelastic pipes with instantaneous low pressures less than saturated vapor pressure,the viscoelasticity of the pipes must be taken into account and the water hammer with column separation must be bridged in order to reflect the actual pressure fluctuations in the pipe and it can improve the accur acy of the gas-liquid two-phase transient flow model of viscoelastic pipeline by correcting the friction model.When the improved IAB friction model is introduced,the relative error of the amplitude value of pressure wave decreased to 3.56%~7.14%.In this paper,the pure liquid phase and gas-liquid two-phase transient flow model of viscoelastic pipe are established.Based on the experimental results in the literature,factors such as the viscoelasticity of the pipe,the pipe-wall constraint coefficient,and the different friction model,etc.,are analyzed.It provides a reference for the study of transient flow in viscoelastic pipes.