Study On The Effect Of Journal Form And Position Errors On The Stable Operating Mechanism And Characteristics Of Liquid Lubricated Bearing Rotor Systems

Hydrodynamic journal bearings are widely used in machinery,power,aerospace and other engineering fields,as the basic component of rotating machines.However,the stability and related dynamic characteristics of the journal bearing system have a profoundinfluence on the safe operation of rotating machinery,and it is also very important for the design of modern journal bearing systems.From the view of manufacturing,the manufacturingerrors of a journal bearing system are inevitable due to the limitations of manufacturing technology and accuracy.Although the absolute size of manufacturing errors of a journal bearing system is very small,when compared with the bearing clearance it is large enough to generate remarkable effects on system operating performance.Although there has some limited research on the effect of manufacturing errors on the performance of hydrodynamic journal bearing system,however,the work is isolated and focus on the effect of dimensional manufacturing errors.Due to the limitations of existing models and calculation methods,the studies of the influence of form and position errors on the operating characteristics of bearing rotor system have not been systematically and effectively carried out.In order to present the effect of the manufacturing tolerances on the dynamic performance of journal bearing system,and to comprehensively and systematically improve the study on the influence of journal manufacturing error,this thesis establishes an analysis model for the journal surface profile and the misalignment of the bearing,presentsa dynamic modelling,analysis,calculatingand experimental method for the hydrodynamic journal bearing system considering journal form and position manufacturing errors,and examines the effect of the errors on thesystem performance.The journal form and position manufacturing errors include the journal roundness error,cylindricity error,surface waviness and the misalignment between rotor axis and bearing axis due to the assembly accuracy.The influence law of the journal form and position error on the system operation characteristics is revealed and the influence relation is evaluated.The main research contents and contributions of the thesis are presented as follows:(1)The study presents an analysis model for the journal surface profile and the misalignment of the journal bearing system.Based on the widely accepted method of Fourier series for roundness error modeling,Legendre polynomial is introduced as an axial description function to represent the axial profile of cylindrical elements.Monte Carlo method is used to simulate random variables and Fourier transform is used to construct uncertain shape errors.The oil film thickness calculation model of the system allowing for the misalignment angle is deduced.The established error calculation model can be directly applied to the analysis of the performance characteristics of the bearing rotor system to fully express the influence of form and position errors.(2)The study presents a dynamic modelling,analysing and calculating method of the rotor bearing system considering the journal form and position errors to study the nonlinear oil film force calculation,system stability analysis method and to examine the effect on the system performance.Based on the proposed method,the effects of journal roundness and cylindricity errors,surface waviness and misalignment angle errors on the stability,load capacity and energy loss of the rotor bearing system are studied.The results show that: the journal form and position errors havenotable influences on the system performance,so they cannot be ignored.Different types of form and position errors affect the system in different ways and degrees.The journal roundness error,cylindricity error and surface waviness are able to promote the system stability and load capacity in certain extend,but may simultaneously increase the system energy loss and generate high frequency vibration components and result in high level vibration of the journal,and the effect of journal out-of-roundness is more significant.However,the misalignment error will reduce the system stability,but to some extent,it is beneficial to improve the bearing load capacity,and the effect of the misalignment error on the bearing load capacity is more remarkable than the other errors.The study also finds that: when the Sommerfeld number S is between 0.02-0.1,the influence of journal macro form errors on the system stability is small,while the influence on the system load capacity decreases when the Sommerfeld number S is greater than 1.0.Therefore,the study suggests that,for a design of a high speed and low load journal bearing system,the Sommerfeld number S should be chosen within 0.02-0.1 to minimize the effect of journal form and position manufacturing errors on the system stability;while for a design of a low speed and heavy load journal bearing system,the Sommerfeld number S should be greater than 1.0 to minimize the effect of journal form and position manufacturing errors on the system load capacity.(3)The study presents adesign and experiment method of a test rig to measure the dynamic characters of the journal bearing system allowing for journal form and position manufacturing errors.The experimental investigation also presents an experimental assessment method of the oil film stability to satisfy the needs of theoretical analysis,calculation result verification and experimental analysis.The experimental results on the effect of journal roundness error,which is more significant,show a good correlation between the theoretical results and experimental results,and also find that the journal roundness error is able to promote the system stability but generate high frequency vibration components and result in high level vibration of the bearing.Therefore,the study presented in this thesis can help engineers to better understand and evaluate the effect of journal form and position errors due to the manufacturing or the wear in the operating stage on the dynamic performance of journal bearing systems,and thereby to more reasonable design and control the manufacturing tolerances.At the same time,the study can help engineers to more accurately predict the operating characteristics of the system with consideration of the structural shape or position deviations due to wear or other reasons,so that the rotor bearing system can operate more safely and reliably.