Study On The Performance Of A Helico-axial Gas-liquid Multiphase Pump Under Slug Flow

Helico-axial multiphase pump is most commonly applied in the areas with tough environment such as offshore and desert oil fields.In general,the crude produced from the well is a mixture of oil,gas,and water.However,the gas content of inlet flow under the well in production applications is varied.Even the slug flow condition might be witnessed.Since unsteady inlet flow conditions could lead to fluctuations in the pressurizing and torque of the multiphase pump as well as reduction in the operating reliability of the multiphase pump system,an independently-designed three-stage helicoaxial multiphase is studied in this paper with the mixture of air and water as its working medium.To be specific,the slug inlet flow condition with the GVF ranged from 20% to80% at the entrance is configured.Unsteady flow simulation and numerical calculation of fluid-solid coupling inside the multiphase pump are carried out.On this basis,the motion state of the gas-liquid two-phase fluid inside the multiphase pump and the stressstrain variation law of the impeller pressurization,torque and of pump shaft are discussed under such a slug inlet flow condition.Firstly,an internal fluid domain model is established for the three-stage helico-axial multiphase pump in order to conduct the unsteady numerical simulation on the gas-liquid two-phase flow in the multiphase pump.In this way,unsteady features of the gas-liquid two-phase distribution and the impeller torque in the pump under the slug inlet flow condition can be analyzed.According to the study,when the multiphase pump is affected by the air plug in the slug inlet flow,the pressurization and torque of impellers at all levels are varied significantly.Besides,as the air plug flows from the inlet to the outlet,the pressurization and torque of the first-stage,second-stage,and third-stage impellers are dropped abruptly in turns.And as the gas content in the pump is reduced with the flow of air plug,the pressurization and torque of impellers at all levels rises up rapidly.The GVF in different impeller is varied due to all-level impellers being affected by the air plug.Of which,the GVF in the first-stage impeller decreases rapidly and then stabilizes.The second-stage impeller increases first and then decreases,and the third-stage impeller increases first and then decreases slightly and then rapidly increases.Secondly,a solid domain model is constructed for the rotating system of the multiphase pump.The deformation and stress distribution of components of the main shaft and impellers at different moments are analyzed under the slug inlet flow condition using the fluid-structure interaction.The study shows that the maximum deformation quantity of the main shaft is firstly increased and then decreased under the influence of the medium and big air masses in the slug inlet flow,and its maximum value is increased by 10.9% in comparison to the stable flow with low gas content.Although the distribution of stress and deformation on the blade of impellers at all levels of the pump remains unchanged,fluctuations can be found in the maximum stress and deformation of the blade.If the slug inlet flow lasts for a long time,it will exert a significant adverse effect on the security in the stable operation of the pump.Research achievements obtained from this paper deepen the understanding concerning the unsteady characteristics of the helico-axial multiphase pump under the slug inlet flow condition,providing a theoretical reference for the design of the slug flow early warning system and the improvement of the security in the multiphase pump operation.