Research On The Positive And Reverse Design Of Twin Screw Profile Based On NURBS

Double screw compressor has been widely used in various fields because of its excellent compression performance.The key parts are a pair of rotating screw rotor.In the domestic,there is no outstanding product facing competitive market in the design of screw rotor.What the engineers’ relentless efforts are aimed at is to break the foreign technology monopoly and seek better performance of the screw rotor profile.This paper mainly studies the innovation design of rotor type line.The design of rotor profiles based on NURBS is studied in depth according to the basic structure and working principle of twin screw compressor.This paper analyzes and designs the NURBS configuration of the rotor type line from both positive and negative aspects.Against the disadvantages of traditional curves that the design of rotor type line cannot be adjusted locally,the non-uniform rational b-spline is incorporated into the configuration of the rotor type and the meshing line.It increases the flexibility of the profile curve of the rotor and realizes the function of local regulating line.It further improves the performance of the rotor type line and further improves the compression performance of the screw compressor.In the process of designing the rotor type of free curve,the conjugate curves of the free curve rotor line are obtained by using the auxiliary Angle formula.In the study of NURBS algorithm,the corresponding algorithm program is designed,the structure of arbitrary free curve and the free curve fitting based on arbitrary discrete points are realized.The structural elements of NURBS curve are analyzed in a comprehensive way.It is specific to NURBS to build the basic curve processing method,including the setting of the node vector and weight factor.In addition,the modification method of NURBS curve is analyzed in detail.The NURBS expression form of screw rotor is derived,including the solution method of NURBS conjugate curve and the NURBS curve enveloping condition in the reverse design of the shape line.It provides the theoretical basis for the optimization of the compressor screw rotor.At the same time,this paper makes a deep analysis of the basic geometry algorithm of NURBS,which covers the node insert,refining the NURBS curve,node elimination and rise order algorithm has carried on the detailed studies.The paper derives the NURBS expression of conical transversal and round,and design corresponding algorithms for different kinds of arc curves.A function file for data exchange standard IGES is prepared,which facilitates the data export of NURBS curve surface.In addition,based on the research foundation of NURBS curve,the construction of NURBS surface is realized by using the NURBS geometric algorithm,which facilitates the geometric modeling design.In order to realize the simple design of screw rotor and be convenient to write the CAD program of rotor type line,the optimal design and performance prediction of screw rotor are further completed.Based on the commonly used screw rotor,this paper explores the commonexpression equations of common curve types.It adapts to the computer aided design of screw rotor type line and improves the design efficiency of rotor type line.The decentralized processing method of universal equations is introduced.By means of discretization of the rotor type linear equation,the rotor type curve can be discretized into a point set to form the discrete coordinate form of the rotor type line.And By using the free curve,the discrete point set can be fitted to form a complete free curve structure of the segmented rotor.The rotor type of the screw compressor is divided into two functional segments: the transmission side and the sealing side.An in-depth study is carried out on the composition curve type of the transmission side line,and the transmission performance of different curves is compared and analyzed.By deriving the curvature expression and sliding rate of different curves,the transmission performance of the transmission side line is determined.Based on the dynamic analysis,the mechanical properties of the drive side curves are described,and the good transmission characteristics of different curves are integrated into the design of the rotor type line.It can effectively improve the stability of the meshing transmission of the screw rotor,thus ensuring the smooth and efficient operation of the screw compressor.The factors that affect the performance of compressor are studied based on fluid dynamics,and the influence of working parameters and structural parameters on the performance of compressor is discussed.It mainly includes: pressure field analysis and velocity field analysis to reveal the flow pattern of flow field in compressor.The influence of speed,pressure ratio and meshing clearance on compressor performance was studied,and different working conditions were set up to analyze the change of compressor compression performance when different variables were changed.Based on the one-dimensional unsteady compressible flow theory,the control equations describing the pulsation of the exhaust cavity of twin screw compressor are established.The numerical solution of the one-dimensional unsteady conserved equations is analyzed,and the test value is compared with the theoretical value through the pressure pulsation test of the twin screw compressor.Lastly,the performance of the screw rotor and the original line based on NURBS design is compared.The screw compressor designed theoretically is simulated by CFD.The performance of the improved compression is determined by the fluid simulation.Finally,the experimental test platform of twin screw compressor was built,which verified the reliability and correctness of theoretical design and fluid simulation.