Research On Bubble Trajectory And Vortex Evolution Law Of Helical Axial Multiphase Flow Pump

Oil and gas two-phase mixed transportation technology is one of the innovative technical directions for the exploitation and transportation of marginal oilfields and deepwater oilfields,and the helical axial flow multiphase flow pump is the key equipment for oil and gas exploitation.Its advantages are that it can simplify the process and realize the pressurization and transportation of multiphase fluids;it is insensitive to solid particles in the fluid and can operate in relatively harsh environments;it can transport multiphase fluids with high gas content and large flow rate fluid.However,most of the research on multiphase flow pumps at this stage focuses on improving the structure of multiphase flow pumps to obtain higher external characteristics.However,there are few studies on its internal flow structure.In order to obtain a more efficient transportation efficiency,the research on its internal flow problem is the only way.This paper takes the single-stage compression unit of the helical axial flow multiphase flow pump as the research object,and adopts the combination of three methods of multiphase flow design theory,experimental observation and numerical simulation.The main research directions are as follows:Firstly,the helical axial flow multiphase flow pump test bench system is introduced,including the components of the test system,the purpose and content of the test,the operation process,the test plan and the analysis of the performance test data.The performance test results show that the increase of the number of compression units can effectively increase the overall supercharging performance of the multiphase flow pump,and the supercharging performance of the latter stage is greatly improved compared with the previous stage.In order to enhance the supercharging capability of the first-stage supercharging unit,it is necessary to adjust the physical parameters of the inlet two-phase medium.When the pure water medium is transported,the proper increase of the rotational speed can significantly improve the boosting capacity of the multiphase flow pump,and the high rotational speed will lead to the enhancement of the system resonance noise,which will harm the safety and stability of the test.When two-phase flow medium is conveyed under the condition of high gas content,the input power of the multi-phase flow pump shows a downward trend until the "gas block" occurs,and the pump cannot flow.Secondly,due to the different densities of the two-phase medium and the different motion trajectories,the gas flows in the form of bubbles,and the change in size and shape during the flow process can intuitively reflect the changes in the fluid parameters in the pump.The results show that: when the rotational speed is below 1200r/min,the volume of the bubbles reaches the maximum at 1/2 of the impeller blade bone line,and the bubbles contact the pressure surface and move toward the suction surface.In the guide vane,the energy of the bubble itself is insufficient to start backflow against the pressure gradient,and the flow condition of the multiphase flow pump is poor.When the rotation speed is above 1450r/min,the number of bubbles in the impeller increases and the size decreases,and the tip clearance begins to flow back with increasing intensity,and the intensity of movement across the runner also gradually increases.There is obvious bubble collision in the tip clearance and the formation of tip clearance vortex.The bubble movement of the bubbles in the guide vane across the flow channel causes gas vortices to appear at the trailing edge of the outlet.With the increase of the rotation speed,the area of the flow channel increases,which hinders the flow of the two-phase flow.Finally,the evolution law of the vortex in the multiphase flow pump is analyzed by changing the input parameters of the helical axial flow multiphase flow pump and the summary of the high inlet gas content observation experiment.As the inlet gas volume flow rate increases,the gas volume fraction in the vortex increases.Gas is easy to accumulate in places with lower pressure,the degree of gas-liquid separation increases,and the volume of vortex in the flow channel increases continuously.With the continuous increase of the rotational speed,the pre-swirl at the dynamic and static interface interferes with the inlet two-phase fluid.There is a sudden change of velocity at the interface between the impeller and the guide vane,and the gas phase is easy to gather near the trailing edge point of the impeller blade and the leading edge point of the guide vane blade.The gas vortex makes the two-phase fluid flow back at the outlet of the impeller,and the flow area near the inlet of the guide vane is reduced.Appropriately increasing the rotational speed can restrain the separation degree of the two-phase fluid in the multiphase flow pump.When the bubble diameter increases,the gas phase gathers near the suction surface of the impeller,but it has little effect on the movement of the mainstream.In the guide vane,the vortex intensity of the tip clearance increases continuously,which has a greater impact on the mainstream movement in the flow channel,and the exit wake presents a "twist" shape,which increases the hydraulic loss of the fluid.With the increase of the flow rate,the inlet conditions are effectively improved and the two phases are mixed evenly,and only part of the interface generates a backflow vortex.The volume ratio of the vortex in the guide vane is also significantly reduced,so the separation phenomenon of the two-phase fluid is improved by increasing the flow rate,and the conveying efficiency is increased under the large flow rate in the high-efficiency area.