Research On The Flow Field And Mechanical Properties Of The Double-head Balanced Twin-screw Pump

Double-screw pump as a fluid driving device has a long history of development,and it is widely used in various industrial fields,such as shipping,oil extraction,paper making,military,medicine,mining and environmental protection.And it has played a huge and irreplaceable role.Double-screw pump has the advantages of self suction performance,good suction performance,the ability to work at higher speeds,not sensitive to the viscosity of the medium,high efficiency and reliable operation.But double-screw pumps used on ships are highly influenced by many factors,such as the characteristics of oil transported,the pressure and flow rate,the temperature and the long maintenance pump period.These factors have high requirements on the structure,assembly method,power output and service life of the prunp.Therefore,it has the certain theoretical significance and important practical value to optimize the existing double-screw pumps and research high-performance double screw pump of ships.In view of this,the paper will analyze and research the double-screw pump from a few aspects.1.The screw rotor is an important part of the double-screw pump.The type of the end face line and the geometric structure parameters of the screw directly affect the performance parameters of the pump.In this paper,a type of the end face line formed by the long external cycloid,the common cycloid and circular arc line is selected.Analysis of the influence of geometric parameters of screw rotor(circle radius of tooth topr3,depth of spiral h and helical guide T)on theoretical flow and leakage of screw pump.And gives the range of parameters,as to prepare for the subsequent optimi-zation design of the rotor structure.In order to facilitate the rapid three-dimensional modeling of subsequent structural optimization,a user interface program for quickly drawing the end face line was designed using MATLAB,which provides an effective tool for the optimization of the whole machine structure of the screw pump.2.Since the working medium of the double-screw pump makes a spiral motion in the pump,it is very difficult to study the law of motion using the experimental detection method.In this paper,based on the theory of computational fluid dynamics,a finite element model of the internal flow passage of a double-screw pump is created.The research of the internal flow field of the pump to obtain the pressure and velocity fields of the moving fluid through professional CFD fluid analysis software.These analyses reveal the characteristics of fluid movement in a double-screw pump.Be-sides,under the condition that the theoretical flow rate of the screw pump and the overall external dimensions are unchanged,the spiral rotor depth and spiral lead of the screw rotor are optimally de-signed with the goal of the highest volumetric efficiency.Finally the flow field analysis of the opti-mized structure was carried out and the distribution changes were observed before and after optimi-zation of the velocity and pressure.3.Due to the long-term operation of the double-screw pump at high rotational speeds,the pre-cision of the design,manufacture and assembly of moving components including screw rotors is very high.Sometimes due to improper design,manufacture and assembly,it may cause the situation where the two screw rotors or the screw and the pump casing are touched or even stuck.This re-duces the working performance and service life of the pump.Therefore,based on the results of the flow field analysis,this paper studies the dynamics of the moving components of the double-screw pump.The numerical simulation method is used to obtain the axial and radial deformation diagrams of the screw rotor and the variation curves of the maximum deformation nodes in these two direc-tions.The relationship between the stress and deformation of the screw is modeled.The reference is given for optimizing the improvement of the clearance between the two-screw rotor and the clear-ance between the screw and the pump housing.4.Before the double-screw pump is put into use,it needs to test its performance(including flow,pressure,etc.).In addition,after the entire pumping station is built up,vibration testing is per-formed to determine whether the vibration level is within the standard range.This prevents the vi-bration from affecting its performance and even results in the loss of workability of the entire pump station system.In this paper,the vibration simulation of the whole double-screw pump was analyzed.The vibration simulation analysis included constrained modal analysis and harmonic response anal-ysis.Finally,the vibration test experiment of the optimized and improved pump was carried out by establishing the test platform of the double-screw pump vibration test.The vibration level of the pump is evaluated by combining the experimental results with the simulation results.