Numerical Simulation Study On Pressure Flow Currently Rush Air-mass In Long Distance Water Supply Pipelines

With the rapid development of various fields in our country, the contradictionbetween the demand for water and the scarcity of water resources has been intensified,daily life, agricultural and industrial in some cities can't get enough water as a result ofthe lack of the water source nearby. Therefore, many cities have started building a lot oflong water pipes to make water source can be transferred from places far away. Amongthese long-distance pipeline projects, some pipelines can reach a length of tenkilometers due to the long distance, some pipelines has become tortuous or different indegree due to crossing some mountains or regions of changing greatly ground. Typically,it's likely to accumulate air-mass in different sizes in some bending of pipeline, the topplace, valve place, and the end when filling water to the pipe, these air masses will notonly affect the efficiency of the water piping system, it will instantly emerge a largeabnormal pressure nearby when there comes a sudden increase in the power of the pumpor the valve pipes suddenly abrupt which looks like a strong incentive to the air mass,and if the abnormal pressure is so high to make pipes burst more easily. So, such studieson gas-liquid two-phase transient flow in the pipeline are very meaningful.Firstly, the theory of gas-liquid two-phase flow and computational fluid dynamicssoftware has been introduced in detail in this paper. Then to find a suitable experimentaldata to check VOF model of Fluent software, through inquiring a lot of documents andengineering examples in connection with pressure flow currently rush air-mass in thepipelines. Finally, to build the representative physical model of pipeline, numericallysimulate the changing course of pressure flow currently rush air-mass with checkedVOF model, then to analysis and predict the change regulation of emerginginstantaneous pressure when air-mass has been rushed currently by pressure flow, so asto provide reference when meets some corresponding problems in long pipelineprojects.Through numerical simulating dozens of conditions which includes different initialpipe pressures, different diameters, different initial volumes of air mass and differentinitial forms of air mass and so on, it shows that transient pressure peak produced bypressure flow rushing air-mass is the most when the volume fraction of the air mass isabout1%of the pipeline. At the same time, keep the initial volume of air-mass, changeinitial volume form of air-mass which means changing void fraction of pipecross-section (initial length of air-mass) with the help of path function in VOF model,we can find that, instantaneous peak pressure is basically the same when the gas accountpipeline cross-section for more than50%, and instantaneous peak pressure decreasinglyaccurate when it is under50%. Through observing and drawing relation curves between the volume of air-mass and air pressure, time, the gas transient process can be dividedinto four sub processes, namely: large amplitude compression process, small amplitudecompression process, small amplitude expansion process, and greatly expanding process.We can calculate that the range of n is different by means of regression analysis methodand the gas changing equations.