Research On The Critical Flow Velocity Of The Bubbles Start To Move In The Pump Pressurized Long-distance Water Pipeline

In recent years,with the rapid development of China s economy,the problem of water resources has been highlighted again.The spatial distribution is more east than west,and the time distribution is more in spring and summer,and less in autumn and winter.In order to solve the related problems of water resources,China has built many large water conveyance projects.At present,due to the small loss and low pollution degree of the water conveyance mode of the pressurized pipeline,it is more and more widely used.The safe operation of water conveyance project plays a vital role in the water supply for residents and industrial water supply.However,under some adverse conditions,the dissolved gas in water will escape.At the same time,in the operation of the project,the water pump and air valve will passively inhale some gas,resulting in the gas remaining in the pipeline to form an air bag.The gas stagnation in the pipe will have many adverse effects on the safe and stable operation of the water conveyance project : reducing the effective flow area of the system,increasing the head loss,and reducing the water conveyance capacity of the system.In severe cases,it will even induce the water hammer to cause the pipe burst,resulting in water supply interruption and other accidents.It can effectively prevent the occurrence of pipe burst accidents by flushing the bubble out of the pipeline before it does not form an air bag.Based on the existing research theory of large-scale bubble starting critical velocity,the calculation formula of bubble starting critical velocity in pump pressurized water pipeline is proposed and verified.The main contents are as follows :Based on the theory of bubble dynamics and fluid mechanics,combined with engineering practice,the motion state of bubbles in the pump pressurized water pipeline is analyzed,and the force model of bubbles and airbags in the pipeline under different sizes and the formula of bubble starting critical velocity are established.Under the guidance of theoretical research,the physical test model of bubble starting in pump pressurized water pipeline is established.The bubble parameters and starting critical velocity data under different working conditions are obtained by using image acquisition system and data acquisition system.The theoretical formula is corrected by comparing and analyzing the theoretical research results.A threedimensional geometric model with the same parameters as the physical test model was established,and the CLSVOF coupled two-phase flow model was selected.The Fluent software was used to carry out the numerical simulation with the same parameters as the physical model test.The flow pattern,flow field and critical starting velocity of the bubble were analyzed,and the results were verified with the physical test results.The conclusion is highly consistent,which proves that the numerical simulation model of this study is reliable.In this paper,the process of bubble starting in the pump pressurized water pipeline is studied from three aspects of theoretical research,physical model test and numerical simulation.A reliable formula for calculating the critical velocity of bubble starting is obtained,which has certain value for promoting the theoretical research of bubble dynamics and has certain guiding significance for the flow rate scheme of pressurized water transmission project.