Study On Flow And Thermal Characteristics Of Shear Flow Of Cross-scale And Variable Cross-section Clearance Between High-speed Rotating Rotor And Stator

China has vast territorial lands and waters.In the new era and under new situations,higher requirements are raised for better maneuverability and longer radius of flight of aircraft.How to continuously promote the reliability and high power-to-weight ratio of the high-speed rotating mechanical equipment system onboard aircraft is an urgent problem ought to be solved.The gaslubricated journal bearing(GLJB)is a new type of rotating mechanical equipment support element with lightweight,strong self-adaptability and many other advantages,which is thought to be an ideal choice,and becomes one research hotspot.However,when under high-speed rotating operation conditions,the flow and thermal characteristics of the shear lubricant gas flow field existing in the variable-section and multiscale clearance are quite complex.Due to the formerly lack of applicable multiscale research methods,and the relatively late starting of domestic research,the understanding of the mechanisms and variation laws of flow and thermal characteristics is limited.The problems of load capacity decline,aerothermal ablation,and thermally-induced operating instability,which have adverse effects on the mastery and promotion of the independent engineering design and operation optimization capability,still need to be better solved.In this dissertation,the multiscale-scale numerical models of the flow and viscous heat dissipation characteristics of shear flow field in clearance of GLJB are established.Besides,the static characteristic and dynamic characteristic numerical models of the multi-leaf gas foil bearing with backing bump foils(MGFB)are built.In addition,as a comparison,the thermal-flow coupled model of ultra-thin lubricant film in the clearance of liquid-lubricated journal bearing(LLGB)is also established.The numerical algorithms of all these models are proposed.The influence mechanism and change rule of the flow and viscous heat dissipation characteristics of the lubricant shear flow,and the static and dynamic characteristics of bearing under different geometric,operational and material parameters are systemically investigated.Both the slip effect and the temperature gradient effect are concerned.Moreover,a test platform is designed and built,with which the flow and thermal properties of shear flow field are researched.The numerical simulated and experimental results are compared,analyzed and verified.(1)A multiscale numerical model and calculation method based on the macroscopic Reynolds equation and the mesoscopic lattice Boltzmann method(LBM)is put forward and established,with which,the flow characteristics of shear gas flow field in the clearance of GLJB are explored.The variation laws of lubricant gas film thickness,pressure,velocity and slip velocity distributions under different eccentricity ratios,bearing speeds and Knudsen numbers(Kn)are investigated,and the differences between the results by two methods are compared and analyzed.By virtue of the LBM,the fresh interesting backflow phenomenon in the lubricant gas film in the clearance is observed and its forming reasons are discussed.This multiscale numerical model obtains relatively compact structure,high computational efficiency and independent intellectual property rights.In general,the results by the macroscopic and mesoscopic methods are in good agreement and acting as complement for each other.More specifically,the macroscopic method possesses clear physical meaning,which is suitable for proofing the mesoscopic method results.In contrast,the mesoscopic method breaks the limitation of the continuous medium assumption of the macroscopic method,thus not only the details of flow field but also the flow characteristics under high Kn numbers,which lies in the slip zone and transition zone,can be captured.(2)A multiscale-scale numerical model of the lubricant viscous heat dissipation characteristics of GLJB based on the Reynolds equation and the lattice Boltzmann method is established and the calculation methods are proposed.It newly achieves the multiscale study of the change rules of the viscous heat dissipation characteristics of the lubricant flow field of GLJB.The influence mechanism and change rule of different bearing speeds,bearing loads,Eckert numbers(Ec),eccentricity ratios and clearance ratios on the viscous thermal dissipation and temperature distributions of the shear lubricant field are researched.The functions of the slip effect and temperature gradient effect are emphasized and analyzed.The multiscale numerical model possesses relatively compact structure,high computational efficiency,and independent intellectual property rights.The macroscopic and mesoscopic methods corroborate with each other,by which valuable viscous heat dissipation and temperature characteristics of complex lubricant flow field in clearance of GLJB have been obtained.(3)As a comparison,a thermal-flow coupled thermohydrodynamic(THD)numerical model of the lubricant film in the clearance of LLGB is established based on the Reynolds equation,energy equation,viscous-temperature and viscous-density equations.The cavitation effect is concerned.The influences of eccentricity ratios,length and diameter ratios,bearing speeds,clearance ratios,and Sommerfeld numbers on change rules of three-dimensional distributions of thickness,pressure,temperature,fluid mass fraction,flow rate and viscous heat dissipation are systemically investigated.Besides,a multi-factor evaluation method is proposed,which supplies reference for the further parameter optimization and performance improvement of the bearings.(4)An elastohydrodynamic static characteristic model of MGFB based on the one-dimensional beam cell model and Reynolds equation method is proposed.The effect of foil deformation is emphasized.Furtherly,a dynamic characteristic model of MGFB is established based on the small perturbation method.The change rules of the clearance shear gas flow characteristics,static and dynamic characteristics under different bearing speeds,eccentricity ratios,length and diameter ratios,bearing numbers,foil thickness,foil Young’s modulus,foil leaf numbers,foil Poisson’s ratios and perturbation frequencies(dynamic)are systemically investigated.The numerical model obtains relatively compact structure,high computational efficiency,and independent controlled computation method,which provides theoretical basis and research method for the engineering design and performance optimization of MGFB.(5)A test platform for the study of flow and thermal characteristics of the shear flow field in the clearance of bearing was designed and built.With the thought of modular design being incorporated,the test platform consists of one foundation platform and three types of test modules,with which the pressure,temperature and PIV-based velocity distributions tests of the clearance shear flow field can be implemented correspondingly.The test system obtains simple and reliable structure,as well as,high testing operation safety.In order to verify both the accuracy and reliability of numerical models established in previous chapters,the experimental results are compared with the simulated results.The experimental and simulation results are overall in well consistence with each other,which furtherly verifies the accuracy and reliability of the relevant models established previously.The multiscale models of flow and viscous heat dissipation characteristics of lubricant flow field in clearance of GLJB and the revelant numerical solution algorithm can enrich the train of thought and method of the research of gas lubrication,as well as,thermohydrodynamic problems of GLJB.It realizes the better prediction of the flow characteristics under larger Kn number range,the capture of the details of the flow field and the exploration of the change rule of aerodynamic heat properties,which improving the theoretical system of GLJB.In addition,the intensive studies of static and dynamic characteristic of MGFB can contribute to the enhancement of the bearing performance,the improvement of the engineering design and optimization capability,and the promotion of the further development and application of MGFB.