| Twin-screw multiphase pump is the core equipment of oil-gas transportation technology,which can transport high IGVF(inlet gas volume fraction)working fluid,and the flow rate changes little with increase of pressure.It is applied in the oil-gas mixed transportation system of marginal,offshore and deep-sea oil-gas fields.However,the structure of twin-screw multiphase pump cavity is complex,and volume of working cavity changes continuously during operation.The transient multiphase flow characteristics in the working cavity are not clear,which seriously limits its application and promotion in the oil-gas mixed transportation system.In this paper,double-suction screw pump is taken as the research object.The numerical simulation and Taguchi method are used to analyze and study flow characteristics of the twin-screw pump and influence of different factors on the performance of the twin-screw pump.The main work and conclusions are as follows:(1)SCORG is used to generate the structured dynamic grid of twin-screw pump.The unsteady multiphase numerical model of the double-suction screw pump is established,and full three-dimensional flow field numerical simulation is carried out.The experimental platform of double-suction screw pump is built,and the performance of the screw pump is tested under the pure liquid and multiphase conditions,and the numerical simulation results are verified and analyzed.The conclusions are as follows:under the pure liquid condition,the output flow of double-suction screw pump decreases with the increase of the outlet pressure,and flow experimental value is slightly less than flow simulation value;under the mixed transmission condition,the output flow of the twin-screw pump decreases with the increase of IGVF,and the trend of the simulation value and the experimental value is the same,but greater than the experimental value.The reason of the error is not only the measurement error,but also the wear of the prototype rotor,and the meshing clearance may be larger than the design value(2)Based on the verified numerical model,the numerical simulation is carried out under different outlet pressure and different IGVF conditions.The results show that:The pressure in the screw pump increases step by step from the inlet to the outlet,and the pressure along the screw direction present a symmetrical distribution.The pressure in both working chambers are approximately homogeneous.The pressure drops sharply at the inlet of circumferential clearance and then decrease linearly in the clearance.The pressure of the monitoring point fluctuates periodically,and there is a pressure pulse,which results in a small pressure pulse in the adjacent low-pressure chamber.The gas phase is mainly distributed in the circumferential clearance and radial clearance of the screw rotor,and the leakage in the circumferential clearance at discharge is dominated by the gas phase.Gas accumulation occurred at the pump outlet,and obvious vortices appeared in the pipe interior and wall.The velocity of working chamber is less than the velocity of clearance,and rotation of screw makes velocity of the fluid change gradiently from the root to the chamber.(3)The Taguchi method is used to study the influence of different factors on the double-suction screw pump.The conclusions can be summarized as follows:The factors level combination of highest volumetric efficiency and hydraulic efficiency is radial clearance of 0.1 mm,circum-ferential clearance of 0.1 mm,rotating speed of 1800 r/min,pressure difference of 0.5 MPa,that is A1B1C4D1.The factors level combination of lowest shaft power is radial clearance of 0.12 mm,circumferential clearance of 0.12 mm,rotating speed of 750 r/min,pressure difference of 0.5 MPa,that is A2B2C1D1.The influence of rotating speed on the volumetric efficiency,hydraulic efficiency and shaft power is the most significant,and the influence of circumferential clearance on volumetric efficiency is more significant;the influence of pressure difference on the shaft power is higher than that on the volumetric efficiency and hydraulic efficiency. |
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