Research On Numerical Calculation Of Hydraulic Transient Phenomenon In Urban Water Supply And Drainage Pipelines

Transients flow in sewer pipelines may cause significant structrual damages and poses serious threats to public safety.It may cause by air-water transient flows and rapid filling in horizontal filled pipes with entrapped air.There have been limited studies on partially filled pipes which can not propose mitigation measures in urban strom.In this thesis,the characteristic method combined with the Pressimann slot is used to simulate the transition process of free-surface-pressurized flow in urban flood process.And this study advanced the current understanding of dynamic behavior of entrapped air above tailwater(the initial water column with a free surface in a partially filled pipe)through rigid-column modeling and sensitivity analysis of system parameters,including tailwater depth,entrapped air volume,driving head,pipe friction,and relative length of entrapped air with regard to the pipe..Water and air were considered as incompressible fluid and ideal gas,respectively,and the continuity and momentum equations for water and a thermodynamic equation for air were solved by using the fourth order Runge-Kutta method.Finally,in view of the error of the numerical model,the applicable scope of the rigid model is discussed.Combined with the conclusions of the numerical experiment,the improved non-dimensional determination parameters suitable for the presence of tail water are proposed.The main findings of this study and conclusions from numerical studies was listed as follows:(1)The results indicated that the presence of tailwater can mitigate the peak pressure,as it can be considered to reflect a certain amount of loss of the net driving head.This alleviation effect,however,may be overtaken by other parametric variations accompanied by the tailwater change.However,the peak pressure can increase as much as about 45% for the cases with fixed pipe length,due to the reduction in the initial entrapped air volume.(2)The rise time for the first peak pressure was closely related to pipe friction,whereas the oscillation period(defined as the time duration between the first and second peaks)was virtually irrelevant.It is necessary to pay attention to the difference between the two when discussing the period or making approximate substitutions.(3)In the verification process of partially filled pipes,the numerical simulation results of most working conditions are in good agreement with the existing test results.For the working conditions with large errors,the applicability of the rigid column model is discussed.The applicability of the rigid-column model was discussed,and an indicator was proposed for the assessment.Existing parameters are verified by comparison of experimental values and theoretical values.The evaluation indicator was proposed and verified forpartially filled pipes.When the indicator is larger than 20,the relative difference between the peak pressure estimation and experimental measurements is generally below 5%.