| Oil-gas-water multiphase mixed transportation technology plays a very important role in the exploitation of marginal oil fields and the long-distance transportation of deep-sea oil.The helical axial flow oil-gas mixed transport pump has the dual functions of pump and compressor,and has the advantages of compact structure,light weight,large flow rate and good sand resistance,making it more suitable for conveying gasliquid two-phase flow.The main reason for the damage or failure of the helical axial flow oil-gas mixed transport pump in the project is that the gas-liquid separation occurs due to the asynchrony of the gas-liquid two-phase medium,which causes the pump to fail or even fail to work.Under different working conditions,to study the helical axial flow oil-gas mixed transport pump in the change of the phase separation,through the design test system,and based on the theory of mechanics of fluid flow,respectively study under the condition of two phase flow inside the impeller flow field changes,phase separation was studied for the impeller blade all up and analysis the influence of different flow field of pump energy transfer characteristics.This paper analyzes the helical axial flow oil-gas mixed transport pump.The numerical simulation calculation adopts the Euler two-fluid model and the SST turbulence model,and at the same time adds a visual test test to study the flow law inside the flow field.First of all,the performance of the helical axial flow oil-gas mixed transport pump with different bubble diameters and different inlet gas content was analyzed,and it was found that with the continuous increase of the inlet bubble diameter and inlet gas content,the performance of the pump decreased gradually.At the same time,the flow characteristics in the helical axial flow oil-gas mixed transport pump on each twodimensional cross-section under different working conditions are analyzed.It can be found that the pressure gradient at the front end of the impeller is larger than that at the rear end of the impeller,so the supercharging performance is mainly reflected in the first half of the impeller.And it was found that the smaller the inlet gas volume fraction,the higher the flow conversion efficiency of the liquid in the pump,the larger the bubble diameter,the weaker the flow of gas accompanying the fluid,and the easier it is to cause aggregation to affect the flow area and reduce the boosting performance of the pump.With the increase of inlet bubble diameter and gas content,the flow field in the impeller and diffuser changes gradually,and the inner flow field of the diffuser becomes more turbulent.Secondly,the gas-liquid separation characteristics in the pump under the condition of gas-liquid two-phase are studied,and the phase separation degree of the impeller and diffuser in different directions is analyzed by calculating the monitoring points.The results show that,when the impeller blade is perpendicular to the flow direction,the separation phenomenon of the flow channel near the hub side is more serious than that of the flow channel near the rim.The change trend of phase separation is basically similar along the flow direction.On the back of the guide vane,the pressure gradient difference perpendicular to the flow direction is the main factor causing the phase separation on the back side;In the diffuser work face,the gas-liquid separation of the working face at low gas holdup is mainly caused by the pressure gradient difference perpendicular to the flow direction,and at medium and high gas holdup,it is the combined effect of the pressure gradient difference in the two directions.Thirdly,through the test results,it is found that the gas-liquid separation position in the impeller occurs near the 2/3 of the airfoil bone line,and after the gas-liquid separation,gas mass will be formed and pocket flow is easily induced,and even the gas block-up phenomenon will cause energy loss to the compression unit.Finally,the hydraulic loss of the flow passage of the helical axial flow oil-gas mixed transport pump at different stages is analyzed.It is found that with the increase of the gas content at the inlet,the pressurization capacity of the impeller decreases gradually,and the static pressure drops slightly at the coupling surface.After that,the energy recovery characteristics of guide vanes under different working conditions and different stages were studied.The results show that the static pressure recovery and total pressure loss in the diffuser have periodic changes.The static pressure recovery performance of the diffuser is the strongest when the first-stage pump has 10% inlet gas content,and the static pressure recovery performance is the lowest and the fluctuation is the most gentle when the primary pump has 60% inlet gas content.With the increase of the inlet air content of the secondary pump,the average static pressure recovery value of the diffuser decreases,and the total pressure loss value increases.In triplex pump,the bubble diameter has little influence on the static pressure recovery of the first stage guide vane at 10% and 20% inlet gas content,while the static pressure recovery and total pressure loss of the first secondary diffuser at medium and high gas content are more complicated. |
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