滑动轴承结构参数对转子系统阻尼临界转速的影响

以三油楔固定瓦滑动轴承(不同心)-弹性Jeffcott转子系统为研究对象.在计及滑动轴承刚度和阻尼特性的基础上,通过编程计算,求解了滑动轴承的动特性系数和轴承-转子系统的阻尼临界转速.获得了轴承结构参数--宽径比、最小间隙比和预负荷系数对系统阻尼临界转速的影响规律.结果表明,轴承结构参数对系统阻尼临界转速产生影响;阻尼临界转速高于不考虑轴承阻尼时的系统临界转速;增大宽径比,减小最小间隙比和预负荷系数使系统阻尼临界转速增大.     

基于流固耦合的离心压缩机轴系振动特性分析

为探究滑动轴承结构参数对离心压缩机轴系振动特性的影响规律,以某型离心压缩机轴承-转子系统为研究对象,首先采用多参考系模型、mixture两相流模型、liner层流模型以及UDF程序,利用隐式耦合求解法对考虑黏温特性的滑动轴承油膜流场进行求解,得到油膜流场压力分布进而对转子系统进行了单向稳态流固耦合分析,探究了轴承间隙比、宽径比对轴系振动特性的影响规律。结果表明：(1)油膜压力随轴承间隙比的增大而减小;临界转速随轴承间隙比的增大而小幅度减小,最大降幅为0.89%;轴系稳定性随间隙比增大呈现先减后增的变化趋势,研究轴系在间隙比为0.0014处稳定性最好。(2)油膜压力随轴承宽径比的增大而增大;临界转速随轴承宽径比的增大而增大,最大增幅为6.9%;轴系稳定性并未随轴承宽径比的增大而呈现规律性变化,研究轴系在宽径比为0.8处稳定性最佳。因此,轴承结构参数对轴系振动特性的影响并非是完全规律性的,我们需要根据旋转机械的实际工况选择合适的轴承结构参数。     

大间隙环流中轴承支承的单质量转子系统特征值分析

建立了大间隙环流中动压滑动轴承支承的单质量转子系统运动方程和特征方程，分析了系统参数对特征值的影响。结果表明，动压滑动轴承特性系数（如刚度和阻尼系数）、大间隙环流特性参数（如流体动力质量、壁面摩擦因数和无量纲间隙比）以及单质量转子系统参数（如系统固有频率）对系统特征值有不同程度的影响。结果表明：随着表征轴承刚度特性的ω1的增大，失稳转速增加，最终γ趋近于2，即相当于Jeffcott转子系统，同时临界转速也随之提高；随着表征轴承阻尼特性ζ的增大，失稳转速不变，临界转速提高；随着表征大间隙环流特性的流体动力质量α的增大，失稳转速不变，临界转速下降；随着表征大间隙环流特性的壁面摩擦因数和无量纲间隙比值β的增大，失稳转速和临界转速均不发生变化：随着表征单质量转子特性的固有频率ω0的增大．失稳转速下降．临界转速降低．     

考虑间隙影响的滑动轴承稳定性分析

为了进一步提升轴承的工作性能,以某型滑动轴承为研究对象,建立流体润滑的数学模型,根据压力扰动法得到轴承动态特性系数,并在此基础上求解轴承-转子系统的失稳转速;以轴承间隙为设计变量,利用MATALA进行数值仿真,分析轴承间隙对最小油膜厚度、油膜压力分布、动态特性系数以及失稳转速的影响。仿真结果表明:增大轴承间隙以及减小轴承宽度都会使得最小油膜厚度增加;油膜压力随着轴承间隙的增加而减小;增大轴承间隙会减小轴承动态特性系数的绝对值;增大轴承间隙会减小转子的失稳转速,降低系统的稳定性。     

超高转速齿轮箱轴承-转子系统性能分析及优化设计研究

以可倾瓦轴承-转子系统为基础,仿真计算分析了轴承跨距、轴径及轴承相关参数对轴承-转子系统临界转速的影响,为高速齿轮箱轴承-转子的优化设计提供依据.研究表明,跨距的影响与转速关系密切;轴径超过54 mm后,影响可忽略;间隙比、支点偏移及预负荷系数对1阶、2阶临界转速的影响趋势基本相同,关系曲线分别为线性、对数和指数形式.根据分析结果,设计了60000 r/min齿轮箱,轴承-转子系统通过空载试验,齿轮箱整体性能满足要求.     

轴承参数对平行转子—轴承系统动力特性的影响

在齿轮耦合的转子-轴承系统中,影响系统动力特性的因素很多,只研究了轴承组合形式、间隙比及宽径比对系统失稳转速、涡动比、临界转速及其分布以及系统阻尼特性的影响.发现在该系统中,存在着系统稳定运行的薄弱环节,当轴承组合形式、间隙比及宽径比产生变化时,系统的失稳转速也将产生变化,并表现出不同的阻尼特性.提出了用最小对数衰减率衡量系统跨越临界转速的能力,用涡动比判断哪个子系统首先失稳.     

多瓦预载荷调整对核主泵轴系临界特性的影响

针对高可靠性立式轴系的横向振动问题,以四瓦水润滑导轴承为研究对象,以多瓦预载荷调整为出发点,分析预载荷系数对导轴承静动特性的影响,同时采用模态分析方法计算2种典型瞬态工况下核主泵轴系的一阶弯曲临界转速及模态振型。结果表明:随着预载荷系数的增大,叶轮和下飞轮处的弯曲程度减小,轴系的临界转速升高;当预载荷系数超过0. 4时,临界转速急剧增大,范围迅速减小。     

动静压轴承支撑高速主轴系统基本性能分析

以高速主轴水润滑动静压轴承为基础,在双动静压轴承支撑主轴系统实验平台上,分析转速、供水压力、载荷等基本运行参数对系统基本性能的影响,并采用不平衡轴承质量法识别了系统支撑轴承的动特性系数。结果表明:轴承-转子系统静态刚度随供水压力和载荷的增大而增大;流量随供水压力升高而增大,而随转速变化较小;利用不平衡轴承质量法识别系统支撑轴承的动特性系数与理论一致性。     

四瓦可倾瓦轴承瓦块摆动特性

以第四代核电机组高温气冷堆氦风机导轴承为对象,系统研究四瓦可倾瓦轴承的瓦块摆动特性。理论推导得出量纲一瓦块摆角取决于轴承结构参数、预负荷和偏心率,但是与轴承间隙比、轴颈转速和润滑油黏度无关。数值分析表明:瓦块摆角特性由瓦块与载荷周向相对位置、预负荷和偏心率决定。轴承结构参数确定时,与载荷正对瓦块的摆角曲线的形状取决于预负荷,预负荷小于0.5时其摆角随偏心率增大先增加后减小,预负荷大于0.5时摆角则随偏心率的增大而逐渐减小;与载荷侧对瓦块的摆角在预负荷较小时随偏心率增大一直增大或减小,预负荷较大时则随偏心率的增大先保持不变然后减小。瓦块摆角对最小油膜厚度影响很大,瓦块摆角可能为负值,从而使最小油膜厚度较固定瓦时的最小油膜厚度偏大。研究结果为氦风机安全运行分析提供了依据。     

轴承结合面间隙对转子支承系统动态特性影响

针对目前工程中凭经验通过人为调节滑动轴承结合面间隙来抑制汽轮机转子振动,缺少理论依据的现状,建立考虑滑动轴承瓦壳顶隙、水平侧隙影响的转子支承系统动力学模型,分别采用有限差分法和有限元法分析调节结合面间隙对滑动轴承动特性参数和转子系统振动特性的影响。分析结果表明,随结合面间隙增大轴承的偏心率、各向支承刚度及交叉阻尼分量(c_(yx))呈非线性减小,偏位角呈非线性增加,转子系统前6阶固有频率略微减小,对由转子质量偏心激励引起的振动响应有明显抑制作用,轴承结合面间隙对系统动态特性的影响不可忽略。     

Rotordynamic Analysis of an Oil-Free Turbocharger Supported on Lobed Gas Foil Bearings—Predictions versus Test Data

This article presents the predictions of the rotordynamic performance of oil-free turbochargers (TCs) for various lobed gas foil bearings (GFBs) with the first-generation bump-type configuration and compares these predictions to the measured test data reported earlier. The three-lobed GFBs used for the simulations have increased bearing clearances and mechanical preloads with a fixed minimum bearing clearance, thus yielding larger average bearing clearances and higher wedge effects at the same time. The engine-induced TC housing excitation is found to have no influence on the critical speeds and damping ratios of the rotor rigid modes. The synchronous and asynchronous GFB analyses imply decreases in destabilizing forces for the highly lobed GFBs. The predicted critical speed and damping ratio of the TC rotor supported on the lobed GFBs demonstrate increasing system natural frequency and enhanced rotordynamic stability with increasing mechanical preload. The rotordynamic and bearing analyses of the lobed GFBs validate the beneficial effects of the mechanical preload on the rotordynamic stability of GFBs even with an increased average bearing clearance, which leads to a decreased bearing friction torque as well.     

多叶动压气体滑动轴承静态特性的有限差分算法

多叶动压气体滑动轴承因其结构简单、摩擦阻力低、旋转精度高和无环境污染等优点,在高速离心分离机、空气压缩机和透平膨胀机等旋转机械中应用广泛。为探究多叶动压气体滑动轴承的静态性能,通过数学变换将三叶动压轴承的气体润滑Reynolds方程转化为标准偏微分方程形式,利用有限差分法和超松弛迭代法进行数值求解,研究气膜厚度和气膜压力分布、承载力、摩擦因数和质量流量等静态性能,随偏心率、预负荷系数、轴承数、长径比及瓦块分布位置的变化规律。结果表明：三叶轴承的承载力和轴颈表面摩擦因数随偏心率和长径比的增加而增加,而偏位角和质量流量随偏心率和预负荷系数的增加则呈现出相反的变化趋势;随着轴承数和预负荷系数的增大,承载力和摩擦因数显著提高,偏位角和质量流量则逐渐减小;瓦块分布位置对三叶动压气体滑动轴承的静态性能影响显著,其中瓦上承载方式的承载力、偏位角和质量流量明显高于瓦间承载方式。     

Temperature,pressure and film thickness measurements for an offset half bearing

A fluid film journal bearing test rig with a shaft, 70 mm in diameter, was developed and an offset half journal bearing was tested at five vertical loads and two rotational speeds. The bearing had a length-to-diameter ratio of 1.00, a pre-load factor of 0.51 and an offset factor of 1.0. Loads from 0 to 4450 N and speeds of 2250 and 1650 rev min⁻¹ were tested. On-rotor instrumentation and amplification are used to measure continuous fluid film pressures around the bearing, film thicknesses and journal temperatures. Slip ring telemetry is used to transmit the data to a real time data collection system. External instrumentation is used to measure film pressures and temperatures in discrete locations on the bearing surface, thus, allowing comparison with the on-shaft measurements. The eccentricity ratio and attitude angle are pressure measurements obtained indicate agreement within 5% between the results recorded by the on-shaft and the external pressure transducers. The experimental film thickness, temperature and pressure profiles and journal eccentricity agree with the expected behavior for this bearing type and are presented for Sommerfeld numbers from 0.41 to 2.2.     

Measured Performance of Tilting-Pad Journal Bearings over a Range of Preloads—Part II: Dynamic Operating Conditions

This article presents a comparison of the measured dynamic coefficients of five tilting-pad journal bearings with a range of preload factors. Each bearing had five shoes machined to a journal diameter of 70 mm, length-to-diameter ratio of 0.75, pivot offset ratios of 0.50, and a nominal assembled radial clearance of 81.3 μm. The rocker-backed tilt pads have nominal radial machined clearances of 176.8, 114.3, 91.4, 73.7, and 61.0 μm. These clearances constitute a range of preloads from ?0.333 to 0.540. Tested were both on-pad and between-pad orientations, with respect to applied forces. Dynamic coefficients are extracted from the test rig by applying sinusoidal synchronous forces and measuring the resulting relative journal-to-bearing motion. A range of speed-load conditions was used, resulting in a Sommerfeld number range of 0.1 to 4.5. Measured dynamic coefficients (nondimensional principal and cross-coupled stiffness and damping coefficients) show the influence of preload. For the speed and load conditions included herein, the dynamic coefficients were not strongly dependent on the preload factor. But very importantly the measured results demonstrate the reduced ability of tilting-pad journal bearings to satisfactorily operate in the negative preload regime for the bearings tested.     

考虑螺栓联接结构的轴承-转子系统振动特性分析

针对含螺栓联接结构的轴承-转子系统,建立考虑陀螺力矩及因螺栓预紧力不均匀产生的初始变形量的非线性转子系统动力学模型。采用法求解转子系统运动方程,通过分岔图、时域曲线、频谱及Poincaré映射图研究存在轴承游隙时转子系统的混沌路径,并分析不同初始变形量及轴承游隙对转子系统非线性振动特性的影响,通过试验验证所得结论的准确性。研究表明,当存在轴承游隙时,预紧力不均匀产生的初始变形量增加会抑制低转速下盘的混沌运动,拟周期运动进入混沌运动状态的转速升高,临界转速附近的振动幅值增加,系统混沌路径发生变化;存在初始变形量时,随着轴承径向游隙增大,系统在低转速工作状态下即进入混沌运动运动状态,拟周期运动进入混沌运动状态的转速降低。研究结果可为含螺栓联接结构的轴承-转子系统设计提供理论参考。     

Effect of Lubricant Non-Newtonian Behavior and Elastic Deformation on the Dynamic Performance of Finite Journal Plastic Bearings

This paper presents a numerical study of the performance of a dynamically loaded finite journal plastic bearing lubricated with a non-Newtonian fluid, taking into account the elastic deformation of the bearing. The non-Newtonian characteristics are adopted in this paper through an equivalent power-law. An expression for a modified Reynolds equation is derived in order to obtain the pressure gradient. Elastic deformation of the bearing surface was estimated in a direction normal to the bearing surface using Boussinesq equations. The film shape was modified accordingly and then iterated with the hydrodynamic pressure distribution in the bearing until a convergent solution was obtained. The Reynolds equation was solved numerically, considering three values of the flow-behavior index (n = 0.6, 1, and 1.2) and a wide range of journal speeds, materials, and clearance ratios. Consequently, the finite perturbation technique was used to determine the eight values of oil film stiffness and damping coefficients. By using the dynamic coefficients, the stability characteristics of the rotor-bearing system and the critical speed were calculated. The results show that increasing the flow-behavior index enhances the rotor-bearing system stability. A considerable destabilizing effect is obtained upon decreasing the elastic deformation coefficient.     

支点弹性、阻尼可倾瓦轴承动力特性数值仿真及试验研究

依据考虑瓦块摆动和沿几何预载荷方向微幅振动的可倾瓦轴承完全动力特性的解析模型及其对应的八参数简化动力模型,设计制备了支点弹性、阻尼特性可倾瓦轴承。该轴承通过在瓦块支点与轴承体之间设置弹性垫片,使瓦块支点支撑在弹性垫片上,弹性垫片与轴承体之间存在微小间隙并与轴颈润滑系统共享油路以实现局部挤压油膜效应。根据不同加工工艺,制备了两种形式的新型支点弹性、阻尼轴承,并通过理论计算模拟与试验分析对两种新型轴承的动力特性进行研究。结果表明,支点弹性、阻尼可倾瓦轴承能够增大转子的一临界阻尼,有效提高转子系统稳定性。     

气体动压径向短轴承动力学和分岔分析

径向气体润滑轴承是精确定位以及微旋转机械中的重要部件,其非线性动力学特性对整个器件的稳定性和可靠性具有重要的影响。文中以气体动压径向短轴承—转子系统为研究对象,建立气体轴承—转子系统耦合非线性动力学方程,以轴承数为分岔参数,分析长径比为0.75时在不同初始偏心率条件下,系统动力学特性随转子转速变化的影响。     

Dynamic stiffness and damping coefficients of aerodynamic tilting-pad journal bearings

The dynamic gas–film forces of aerodynamic bearing often can be characterized by eight linear stiffness and damping coefficients. How to theoretically predict these coefficients is a very difficult issue for tilting-pad gas bearing design because of its structural complexity. The current study presents a novel and universal theoretical analysis method for calculating the dynamic stiffness and damping coefficients of aerodynamic tilting-pad bearing. The gas–film pressure within the bearing is expressed in the form of dimensionless compressible gas-lubricated Reynolds equation, which is solved by means of the finite element method. With the assumption that the journal and the pads are disturbed with the same frequency, the dynamic coefficients of tilting-pad gas bearing are computed by using the partial derivative method and the equivalent coefficient method. Finally, the investigations are conducted about the effects of bearing number, perturbation frequency of the journal and the pads, eccentricity ratios, preload and length-to-diameter ratio of the bearing on the dynamic coefficients of aerodynamic tilting-pad journal bearing. The numerical results indicate that the dynamic stiffness and damping coefficients of tilting-pad gas bearing are closely related with these factors. The proposed analytical method provides a valuable means of predicting dynamic performances of tilting-pad gas bearing. The solution can be used for the purpose of prediction of dynamic behavior of the rotor systems supported by aerodynamic tilting-pad bearings.