Air/Water Flow Performance Of Contra-rotating Axial Flow Pump

Deep-sea oil and gas mixing and transmission is an important development direction of modern oil extraction and transmission technology.Compared with the traditional single-phase medium transmission,the density difference and mutual exclusion between the two phases of the medium make the mixed medium produce problems such as gas-liquid separation and gas mass clogging phenomenon under the action of rotating machinery,which put forward higher requirements on the oil transmission system.With the continuous growth of international energy demand,oil-producing countries have been looking for various advanced technical means to improve the utilization of oil resources.The counter-rotating axial flow pump has a more compact design,higher efficiency and good cavitation performance,but little research has been reported on counter-rotating axial flow gas-liquid mixed transport pumps.In this paper,we use Fluent solver,Eulerian multiphase flow model and SST k-ω turbulence model to numerically simulate a counter-rotating axial flow pump in the whole basin,and systematically investigate the gas-liquid mixing characteristics of counter-rotating axial flow pump based on axial clearance and variable speed control method.The conclusions are as follows.(1)The external characteristics of the counter-rotating axial flow hybrid pump were explored and found that when the inlet gas content rate is maintained constant,the head curve of the hybrid pump shows a decreasing trend and the efficiency curve shows a rising and then decreasing trend as the inlet flow rate increases,and the efficiency of the hybrid pump reaches the maximum when the flow rate is at 0.7Qd.The gas phase moves toward the hub side and the liquid phase flows toward the rim side.The gas accumulation phenomenon is more prominent in the rear impeller than the front impeller,and the gas phase always gathers in the inverse pressure gradient region.(2)The mixing characteristics of the counter-rotating axial flow pump based on the variable speed control method are investigated.In the selected speed matching interval,both methods can improve the head and efficiency of the mixed transfer pump.The front impeller speed control method can improve the head of the counter-rotating axial flow mixer pump,and the rear impeller speed control method corresponds to a higher efficiency of the mixer pump.In the variable speed control method,the inverse pressure gradient region of the two impeller stages changes significantly.In the front impeller variable speed control method,the change curves of turbulent kinetic energy and dissipation rate from the inlet of the front impeller to the outlet of the rear impeller are single-peaked curves;in the rear impeller variable speed control method,the change curves of turbulent kinetic energy and dissipation rate are double-peaked curves.Comparing the turbulent kinetic energy and dissipation rate curves of the two speed control methods,it is found that the turbulent kinetic energy curve of the front impeller speed control method is higher than that of the rear impeller speed control method,indicating that the turbulent diffusion is more intense and the mechanical energy dissipation is more serious in the front impeller speed control method.(3)The axial clearance between the front impeller and the rear impeller is the main factor affecting the performance of the counter-rotating axial flow pump.Four sets of axial clearances were selected to investigate the gas-liquid mixing characteristics of the counter-rotating axial flow pump.δ =0.04 axial clearance was selected to achieve higher head of the mixing pump,but the interaction between the dynamic/dynamic interface was stronger,resulting in unstable flow and lower mixing efficiency;δ =0.16,with the increase of the inlet gas content,a local high-pressure area appeared at the dynamic/dynamic interface,resulting in the poor pressurization effect of the rear impeller,thus It is proved that excessive axial clearance will affect the head of the rear impeller,but will improve the effect of the wake effect of the front impeller outlet on the rear impeller inlet,and effectively improve the gas phase accumulation in the flow channel of the rear impeller;δ =0.12,the efficiency of the counter-rotating axial mixed flow pump is better than the other three groups.Therefore,choosing a suitable axial clearance in the counter-rotating axial flow mixing pump can improve the interference effect at the dynamic/dynamic cross interface,reduce the degree of turbulent diffusion and reduce energy loss.