Study On Gas-Liquid Two-Phase Flow In The Phase Of Water Carrying Gas In Siphon Outlet Passage Of Pump Station

Siphon outlet passage is an important part of pump station project.It is widely used in pump station for the advantages such as safe and reliable shutdown.From pump station start-up to completion of siphon formation,the siphon outlet passage will experience three phase,the first is water driving gas phase,the second is water carrying gas phase,the third is siphon completion phase,And The water carrying gas phase last longest,also it is the key to influence the time formation of siphon.If because of the low design flow rate or unrational siphon outlet structure design,leading to that the phase of water carrying gas is too long or even unable to finish the siphon formation,which will bring adverse pump unit vibration,noise and other phenomena,and cause accidents.If the design flow rate is too high,it will also cause the pump unit vibration and,the disorder siphon flow,therefore,it is of significance to study the gas-liquid twophase flow in phase of water carrying gas in siphon outlet passage.Through hydraulic model experiments,it is found that when air volume is the same,the phase of water carrying gas can be divided into two typical water carrying gas states due to different water flow velocity,The effects of descent angle and air volume on the minimum velocity required by different water carrying gas state are investigated;based on the hydraulic model experiments,PIV experiments and gas-liquid two-phase flow theory,dynamics of air pocket and bubble and the water flow field are analyzed,and the results show that the dynamic pressure and viscous force on air pocket could overcome the buoyancy from water,the pressure and the friction from wall is the decisive factor of whether the air pocket can be carried out of the hump as a whole.The main reason for the rupture of air pocket is the high turbulence intensity and strong shear force produced by great velocity gradient,so surface tension cannot maintain the air pocket boundary shape.Through the calculation with the four numerical simulation method the results show that the results of RNG k-ε can best fit the experiment results in many ways.by the analysis of numerical simulation results,it is found that the great velocity gradient cause the air pocket crack from the middle to sides,and the symmetrical eddies appear on the cross sections near broken place of air pocket.Finally based on respond surface method to analyze the influence of the descent angle,rise angle and aspect ratio on the duration of water carrying gas phase.