Investigation On Spatial-temporal Evolution And Enstrophy Dissipation Of The Tip Leakage Vortex In A Multiphase Pump

Energy is an important resource for the survival of human beings and the cornerstone of modern industrial development.With the continuous development of science and technology,abundant oil and gas resources has been discovered in the ocean.After scientific design and experimental verification by experts,a set of perfect mixed transportation system for deep-sea oil and gas resource has been established.The multiphase pump is the key equipment of the multiphase transport system,its safe and stable operation is related to the exploitation for oil and gas resources.Tip leakage vortex(TLV)formed in tip clearance region of a multiphase pump significantly deteriorates the flow pattern,and then increases hydraulic loss,resulting in the decline of energy performance.However,the unsteady evolution of TLV is not studied in a multiphase pump,and the internal mechanism of vortex motion is not yet revealed.In addition,there are few literatures to explore the position,form and influence factors of the energy dissipation from the TLV.Therefore,to reveal the unsteady motion mechanism of TLV and explore the law of energy dissipation during TLV spatial-temporal evolution,the spatial-temporal evolution and enstrophy dissipation were systematically studied in a multiphase pump.(1)The flow pattern of TLV is accurately captured and the vortex structure is carefully analyzed.TLV structures included the leading-edge vortex(LV),tip separation vortex(TSV),primary tip leakage vortex(PTLV),secondary tip leakage vortex(STLV),and trailing-edge vortex(TV)in a multiphase pump.In one impeller rotation period,the3 D spatial-temporal evolution of the TLV could be divided into three stages: splitting,shrinking,and merging.In this process,the spatial-temporal evolution of the PTLV and STLV were closely correlated.The 2D spatial–temporal evolution of the TLV could be classified into three stages in an impeller revolution 8/15T: inception,development,and dissipation.In addition,the relative vorticity transport equation was used to analyze the TLV near the tip clearance region of the impeller.Results showed that the relative vortex stretching item(RVS),Coriolis force(CORF),and viscous diffusion(VISD)jointly controlled the spatial-temporal evolution of the TLV and were the dynamic sources of variation in the vorticity and trajectory of the TLV.In particular,the gas phase changed the distributions of the RVS,CORF,and VISD on the intensity isosurface of the TLV and had a significant effect on the spatial–temporal evolution of the TLV.(2)The location,mode and energy dissipation rate caused by the TLV are determined by using enstrophy dissipation theory.The relationship between vorticity and the enstrophy dissipation rate is summarized,and the energy dissipation law is revealed during the inception,development,and dissipation of the TLV.The present analysis indicates that the vorticity is highest at the core of the TLV and gradually weakens along the radial direction with the vortex core at the center,the enstrophy dissipation,however,presented the opposite distribution law.The enstrophy dissipation rate changes as the spatial-temporal evolution of the TLV.Moreover,the gas phase significantly deteriorates the flow pattern of the TLV,enhances the volume enstrophy dissipation rate,and reduces the wall enstrophy dissipation rate.The volume enstrophy dissipation power increases by 45.33% with an inlet gas void fraction(IGVF)of 10%,the wall enstrophy dissipation power decreases by 23.90%,and the total enstrophy dissipation power increases by 17.21%.(3)The effects of flow rate,tip clearance,and IGVF on energy dissipation cause by TLV were investigated and prediction models are established.The results show that increasing flow rate,tip clearance,and IGVF significantly exacerbate the TLV pattern and raise the TLV scale,which gradually raises volume enstrophy dissipation and decreases wall enstrophy dissipation.As the flow rate increases,the separation angle between the PTLV trajectory and the blade gradually decreases,and widely dispersing the enstrophy dissipation near the shroud.However,as the tip clearance increases,the TSV scale increases and extends to the suction surface,raising the velocity gradient.Besides,as the IGVF increases,the STLV develops from a continuous sheet vortex to a scattered strip vortex,increasing the significantly increasing the enstrophy dissipation.Considering the flow rate,tip clearance,and IGVF as independent variables,simple and multiple nonlinear regression models have the ability to predict the enstrophy dissipation of the TLV accurately.