Investigation On The Effect Mechanism Of Inlet Gas Volume Fraction On The Performance And Internal Gas-liquid Two-phase Distribution Morphology Of Mixed Transport Pump

With the rapid development of national economy and industry,the demand for energy is increasing once for all,and the exploitation of fossil energy is gradually moving towards deep-sea oil and gas resources.The multiphase mixed transport pump has become an important production equipment that can transport offshore oil and gas resources to the land.However,because of the particularity of the Marine working environment and the conveying medium,the internal flow characteristics of the mixed transport pump are extremely complex,and the performance of the pump is greatly affected by the gas volume fraction,the safe and stable operation of the mixed transport pump unit is threatened under extreme working conditions,resulting in immeasurable losses.In this study,the self-developed multiphase mixed transport pump is taken as the research object,and the experimental test system of the multiphase mixed transport pump is established.The gas-liquid two-phase transient flow characteristics research and experimental research of the mixed transport pump are carried out.The gas-liquid two-phase flow characteristics and hydrodynamic characteristics of the pump were investigated by combining numerical simulation and experiment under different gas volume fraction conditions.The main research contents and conclusions are as follows:In view of the backward theoretical design of multiphase mixed transport pump with low specific speed and the poor performance of mixed transport pump with high gas volume fraction.The geometric parameters of the impeller and diffuser were determined by optimizing the impeller structure design and the form of stator-rotor connection.Combined with the numerical simulation results and the gas-liquid two-phase flow experimental results,the relationship between the blade geometry parameters and the performance of the mixed transport pump was analyzed,and the development of the model and prototype of the mixed transport pump was completed.The experimental research on the multiphase mixed transport pump is carried out under pure water condition and variable gas volume fraction condition.The results show that the performance of the mixed transport pump meets the design requirements under pure water and gas-liquid two-phase working conditions.The correlation between the gas volume fraction and the pump head is established,and the reasons for the errors between the experimental results and the numerical results are illustrated.The effect of the rotating speed on the pressurization performance of the mixed transport pump was studied.The results show that increasing the speed can effectively improve the pressurization capacity,but with the increase of the gas volume fraction,increasing the speed is limited to improve the pressurization capacity of the mixed transport pump.Through the full flow channel numerical simulation of the three-stage mixed transport pump,the change process of the transient flow characteristics in the multiphase mixed transport pump is defined.The variation law of relative blade flow Angle at impeller inlet and outlet is analyzed under pure water and gas-liquid two-phase flow conditions.At the same time,the change rule of head and efficiency of mixed transport pump with the gas volume fraction is defined.By analyzing the internal pressure pulsation characteristics of the impeller and diffuser,the relationship between the gas volume fraction and the main frequency amplitude of pressure pulsation in the pressurization unit is revealed.Under the design condition,the variation process of the transient axial force on the impeller and diffuser with the gas volume fraction was revealed,and the function relationship between the average axial force and the gas volume fraction was established,which provided a certain reference for the safe and stable operation of the mixed transport pump.The relationship between the gas volume fraction,the liquid phase flow field parameters and the blade load was established by analyzing the distribution pattern of the internal phase distribution of the mixed transport pump and the change process of the air mass forms.The basic cause of the complicated change of the flow characteristics in the mixed transport pump was revealed.Under the condition of variable flow rate and gas content,the gas volume fraction changes dramatically in the stator-rotor interference region,resulting in the increase of hydraulic losses in the diversion cavity and diffusor.However,increasing the liquid flow rate can effectively improve the gas-liquid two-phase flow state in the diversion cavity and reduce the hydraulic losses.By analyzing the effect of the change of flow rate and gas content on the pressure and flow trajectory of the impeller blade surface,the change rule of the pressure in the impeller and the evolution process of the flow trajectory on the blade surface in the gas-liquid two-phase flow condition were clarified,and then the evolution law of the transient flow characteristics in the mixed transport pump was defined.