| As an impurity pump,vortex pumps have the advantages of simple structure,smooth operation,and good non clogging,and are mainly used in industrial and agricultural fields such as chemical processes,slurry transportation,and sewage treatment.In the process of operation,the pumped fluid often exhibits gas-liquid two-phase flow such as bubbly flow,and the distribution characteristics of gas-liquid two-phase in the flow field are important factors determining the pressure rise characteristics and energy conversion characteristics of the pump.Therefore,studying the gas-liquid two-phase flow characteristics in a vortex pump under bubbly inflow conditions is of great significance for optimizing the structure of the vortex pump,improving the efficiency and stability of the pump.At present,the impact of gas-liquid twophase medium on the performance of vortex pumps is not clear,and related research needs to be carried out.This article is mainly based on numerical simulation methods to explore the gasliquid two-phase evolution process and energy conversion characteristics of a vortex pump under different flow rates and inlet gas volume fraction (IGVF).The main content and understanding are as follows:(1) The flow field evolution characteristics during the transportation of gas-liquid twophase flow by a vortex pump were obtained.The gas-liquid two-phase flow field of vortex pump with inlet gas volume fraction of 1%,5%,10% and 15% was calculated by using the mixture model and the Standard k-ε model using numerical simulation method.The analysis shows that the transportation of gas-liquid two-phase flow medium by a vortex pump has a significant impact on the performance of the vortex pump.When the inlet gas volume fraction is 1%,gas mainly accumulates near the impeller hub to form a agglomerated bubble flow.Compared with single-phase working conditions,adding a small amount of gas to the liquid medium reduces the fluid velocity at the outer edge of the impeller,reduces the vortex area of the circulating flow in the vaneless chamber,and decreases the number of vortex cores.The flow field structure of the vortex pump is improved,which helps to improve the efficiency of the vortex pump.As the inlet gas volume fraction increases,the agglomerated bubble flow in the impeller domain gradually develops into a separated flow,causing gas-liquid separation.At the same time,more gas gradually diffuses into the vaneless chamber.The instability of the gasliquid phase boundary can cause flow field structure disorder,leading to a decrease in pressure gradient and an increase in energy loss,resulting in a rapid decrease in the head and efficiency of the vortex pump.(2) The influence of bubble size and bubble distribution on the transport performance of vortex pump in gas-liquid two-phase flow field was analyzed.The PBM coupling model was used to calculate the bubble size distribution when the vortex pump transported the gas-liquid two-phase flow,and the Luo model was used to discrete the bubble size.The results show that for the bubble flow transport under the inlet pressure of 7MPa,when the inlet gas volume fraction of the vortex pump is 1%,the inlet bubble will be compressed under the action of high pressure in the pump,and the average bubble size of the pump outlet and each flow component will be smaller than the average bubble size of the pump inlet.With the increase of IGVF,the bubble size in the pump cavity gradually increases,and the average bubble size in the vaneless chamber is the largest among the flow components.When IGVF is greater than 5%,the probability of bubble coalession in the pump increases,and the density of large-size bubbles at the pump outlet increases,and the average bubble size at the outlet is larger than the average bubble size at the inlet.At the same time,the flow rate also has an obvious effect on the coalescing and crushing behavior of bubbles.When the pump contains a large number of gas phases (IGVF≥10%),the gas in the condition of small flow rate is more likely to coalescing into large bubbles.(3) The influence of circulating flow structure on the energy conversion characteristics of vortex pump has been explored.The vortex core positions of different axial cross-sections in the vaneless chamber were extracted to characterize the distribution of circulating flow,and the energy conversion characteristics of the vortex pump were analyzed using vortex identification criteria and entropy production principle.The results indicate that with the increase of IGVF,the number of circulating flow increases,and the interference between vortices leads to an increase in energy loss in the circulating flow,thereby reducing the performance of the pump to a certain extent.The circulating flow circulates in the form of vortex strips in the vaneless chamber,where the intensity of the circulating flow near the volute chamber is higher and the vortex strip structure is more stable.However,the intensity of the circulating flow at the small radius of the vaneless chamber is lower,and its scale range varies with the change of IGVF.When the inlet gas volume fraction is greater than 10%,there is no obvious change in the number of vortex cores and the distribution scale of the circulating flow in the vaneless chamber.However,the energy gradient near the volute increases,the stability of the circulating flow structure decreases,and the entropy production loss is high,which results in the reduction of the efficiency and head of the vortex pump. |
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