Theoretical Study And Numerical Simulation Of The Protection Of Water

In recent years, long distance pipelines distributed in the complex and undulating terrain in china increased year by year. This kind of projects is very easy to produce water hammer pressure wave and decompression wave to spread to the upstream and downstream of the pipeline at high speed in some operation processes, such as pump station start and stop, pump unit speed control, the intermediate station process switching or sub transmission station start and stop, accident pump shutdown, regulating valve failure, mistakenly closed and so on.The water hammer pressure wave and decompression wave tends to make the liquid column separation and collapsing water hammer phenomenon in the pipeline, Such phenomenon will cause great harm to the pipeline. So the further research on the block cavity collapsing water hammer and comprehensive protective measures of the block cavity collapsing water hammer is of great significance to ensure the reliable and safe operation of the pipeline.The block cavity collapsing water hammer is a gas-liquid two-phase flow transient flow problem that is very complex and has diverse flow patterns. In this paper, the block cavity collapsing water hammer and its comprehensive protective measures were investigated by analytical study and numerical simulation.(1) Through theoretical research and analysis of the liquid column separation and collapsing water hammer phenomenon, and summary the law of the reduction of pressure and the release of gases, liquid column separation process and its influence factors, the classification of the block cavity, the relationship between the block cavity and the collapsing water hammer from the perspective of micro bubble dynamics and macrograph, to understand the essence and law of the process of the block cavity collapsing water hammer as a whole.(2) Through the research on the working principle, the performance characteristic and the selection technical requirement of common water hammer protection measures of the two slow closing butterfly valve, the air valve, the one-way pressure regulating tower, we summarized the basic data that is needed when choose the comprehensive protective measure for the block cavity collapsing water hammer. Comprehensive protection’s protective target and selective principle of the block cavity collapsing water hammer are proposed.(3) Through the research and analysis of the numerical solution, the solving process of the numerical solution is derived. Water hammer differential equation is transformed into compatibility equation by using the method of characteristic line in order to get the approximate numerical solution. Inner and outer boundary conditions of all kinds working conditions are established to get the mathematical model of general water hammer calculation.(4) The mathematical model of the block cavity collapsing water hammer is established and solved on the basis of the block cavity collapsing water hammer’s theoretical research and numerical solution when take the pattern of the block cavity into consideration: completely block type steam cavity discrete mathematical model and completely block type air cavity discrete mathematical model.(5) On the basis of the mathematical model of the block cavity collapsing water hammer, to compile the numerical simulation’s Calculation program of the block cavity collapsing water hammer combined with the water hammer comprehensive protective measures by using Visual Basic6.0as development language.(6) Taking the pump stop accidently in the practical engineering project that lead to several liquid column separations an example, according to the various block cavity collapsing water hammer’s mathematic model combined with the water hammer comprehensive protective measures in different working conditions, to run the numerical simulation. Through the numerical simulation results, the minimum water head envelope, the highest water head envelope, the water hammer transient curve of main points and other related water hammer data are mapped. The pump station and pipeline system’s whole block cavity collapsing water hammer process was analyzed under different water hammer protective measures. Finally by comparing the effect of various kinds of water hammer protective measures, the study obtained most suitable, secure and reliable comprehensive protective measure of block cavity collapsing water hammer for the project.