汽轮机可倾瓦轴承油膜特性研究

为了研究汽轮机可倾瓦轴承的油膜特性,采用Pro/E建模和ANSYS模拟,选用计算三维模型的湍流SST模型,考虑到瓦块间隙及瓦块相互之间的影响,分析并比较不同瓦数可倾瓦轴承油膜流场的变化,得到可倾瓦油膜特性规律:对于某个瓦块,每个瓦块上的油膜形成一个正压极值中心,且随着瓦块数增加,极值中心向轴瓦支点处偏移,使瓦块上形成两个压力极值。瓦块温度分布较平稳,油膜出口处温升较大;随着可倾瓦瓦块数增加,油膜压力峰值逐渐减小且瓦块之间的油膜压力峰值差减小并趋于平稳,不同轴瓦间油膜温度变化较小。润滑油温升对油膜影响较大,汽轮机运行中可倾瓦四瓦轴承比较稳定,但应严格控制润滑油温升。     

分布式双向可倾瓦动静压推力轴承的静动特性研究

针对机床主轴对推力轴承的高刚度与高精度要求,用可倾瓦块代替部分静压油垫,提出了一种由可倾瓦块和静压油腔联合承载的分布式双向可倾瓦动静压推力轴承.首先建立了分布式双向可倾瓦动静压轴承的润滑模型,提出了基于平衡点性能合成的轴承静动特性计算方法.针对案例轴承对节流器的结构参数进行了优化,分析了载荷、转速、单边间隙和预负荷系数...     

考虑轴颈与轴瓦耦合运动的可倾瓦轴承完整动力学模型的研究

从单块瓦与轴颈组成的子系统在整体坐标系和局部坐标系中的几何关系入手,建立考虑轴颈与瓦块耦合运动的可倾瓦轴承的完整动力学模型。在局部坐标系中,采用二维有限元方法求解油膜力和动力特性系数,通过坐标变换叠加到整体坐标系中从而得到可倾瓦轴承动力特性系数的解析表达式,结合Newton-Raphson迭代法计算给定载荷工况下的轴承的静平衡位置。通过2个计算实例证明提出方法的正确性,同时通过与传统折合动力学模型计算结果的比较,证明可倾瓦非本质稳定的结论。     

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。     

轴瓦热弹变形对大直径重载滑动轴承性能的影响

针对大直径重载实际椭圆轴承进行热弹性能研究,含静特性和动特性,变形影响的讨论主要是个案,并由此适度拓展提出了变形控制思想和初步技术。计算中,采用课题组轴承计算FORTRAN软件和商用ANSYS软件联合仿真考虑瓦块变形下的轴承特性,结果表明:表面弹性变形对轴承的间隙、最小油膜厚度和温度分布等静特性的影响较小;相比弹性变形,轴承瓦面热变形对轴承静特性影响较大,特别是功耗和最小油膜厚度,变形量与最小油膜厚度量级相同。对于较大变形的影响,提出了通过改变瓦块约束方式或结构参数两种控制变形技术来改善轴承性能,这为重载轴承的优化设计和承载能力提升提供了新的思路。因此大直径重载轴承设计时,应考虑轴承在运行时的热效应,转速越高、载荷越大时,热效应越显著。     

考虑扰动频率的可倾瓦轴承动力学建模及数值模拟

可倾瓦轴承瓦块的摆动性增加了系统的自由度,对轴承油膜动力系数计算有很大影响,而目前的研究在计算流体动压润滑可倾瓦轴承油膜动力系数时未考虑轴颈与瓦块扰动频率的影响。针对这一问题,对考虑扰动频率的可倾瓦轴承动力学建模及动力系数计算方法进行研究,提出考虑扰动频率的可倾瓦轴承频率-缩减(Frequecy-Reduced)动力学模型,详细推导考虑扰动频率的可倾瓦轴承频率-缩减油膜动力系数矩阵形式。采用Newton-Raphson迭代法计算给定载荷和转速工况下的轴承的静平衡位置,利用有限元数值方法求解油膜刚度系数与阻尼系数。结果表明,瓦块和轴颈的扰动频率对可倾瓦动压轴承动态刚度和阻尼影响较大,随着扰动频率增大,阻尼系数的直接项增大,阻尼系数的交叉项变化不大;刚度系数的直接项数值减小,交叉项变化不大。     

可倾瓦径向气体轴承的静动特性的理论研究

运用小扰动法和线性PH的思想,采用有限差分亚松弛的数值方法求解了可倾瓦径向动压气体轴承单块瓦的静、动特性方程。通过比较,得出一系列静特性参数和16个动特性参数,并讨论了影响静、动特性参数变化的因素。计算数据表明,轴承数和轴颈偏心率对轴承静态和动态特性的影响较大,并且瓦片参数取值推荐为L/D=1.0,α/β=0.65。     

瓦块固有频率对可倾瓦轴承频变刚度的影响

为研究轻载工况下可倾瓦块固有频率和振动频率对轴承刚度的影响,基于长轴承理论建立求解可倾瓦推力轴承瓦块固有频率和频变刚度的润滑和动力学耦合模型,推导润滑模型的解析解和频变动力学特性的表达式,并通过实例计算分析载荷、支点系数(瓦进油边到支点的距离与瓦长的比值)、瓦块转动惯量等结构参数对瓦块固有频率和频变刚度的影响。结果表明:瓦块的惯性、油膜的刚度和阻尼共同决定瓦块振动的固有频率,瓦块在固有频率附近振动可以使轴承的频变刚度出现负值,甚至正负无穷大;小载荷的瓦(如非承载瓦)容易出现瓦块振动频率接近其固有频率的状况,使瓦发生共振;可倾瓦轴承设计中有必要考虑瓦块的固有频率和频变刚度来设计非承载瓦的支点系数和转动惯量,使瓦块的振动频率跨过固有频率而产生大的刚度。     

可倾瓦径向气体轴承间隙对其静态性能的影响

采用有限差分法求解三可倾瓦径向气体轴承静态气体润滑方程,得到了稳态时轴瓦与转子表面间的气膜压力分布;在一定静载荷下,计算了不同轴承间隙对应的转子起飞转速及相同工作转速下的最高气膜压力;分析了不同轴承间隙时,转速从起飞转速上升至工作转速过程中转子偏心率和瓦块摆角的变化。结果表明:在一定静载荷下,轴承间隙越大,轴承的最高气膜压力越小,转子的起飞转速越高,偏心率及各瓦块的摆动幅度越大。     

可倾瓦轴承的完整动力分析模型及计算方法

提出求解可倾瓦径向滑动轴承完整动力特性的解析模型和计算方法,给出可倾瓦轴承完整动力特性系数矩阵的简明表达形式.基于瓦块和轴颈间的运动耦合关系,建立瓦块局部坐标系统.与瓦块和轴颈运动相关的全局广义位移矢量可以通过简练的步骤转换为局部动坐标系下轴颈的位移矢量;利用求解固定瓦轴承动力特性的方法求得的局部动坐标系下的油膜力及其Jocabian矩阵,该油膜力矢量可以精确地转换为全局广义坐标系下的表达形式.在轴承的平衡位置处,全局坐标系下的油膜力矢量关于广义位移和广义速度的Jocabian矩阵为轴承完整动力特性系数矩阵的负值.给瓦块一个设定的扰动频率,就可以得到简化的当量动力特性系数矩阵.此解析方法求解简单方便,可用于分析可倾瓦轴承-转子系统.     

高档数控机床静压转台双环形油腔流场特性仿真

为了提高高档数控机床的加工精度和稳定性,设计了一种新型的双环形油腔结构。基于流体动力学理论,并采用计算流体动力学(Computational Fluid Dynamics,CFD)数值模拟方法,研究了入口雷诺数对油腔内部流场结构和油腔承载力的影响。结果表明:入口雷诺数对于油腔内部流场结构和油腔承载力均具有重要影响;随着入口雷诺数的增大,油腔中心凹槽内部由单胞对流发展成多胞对流;同时,油腔承载力也相应增加。通过与传统圆形油腔对比发现,在相同入口雷诺数条件下,双环形油腔具有更高的承载力。该研究对设计高档数控机床新型油腔结构、优化油腔几何结构、提高承载力和加工精度有指导意义。     

An analytical model for complete dynamical coefficients of a tilting-pad journal bearing

An analytical model as well as calculation method is presented for the complete dynamic characteristics of tilting-pad journal bearing. Using this model, the global oil-film forces, stiffness and damping coefficients acting on the journal and all pads can be calculated in a highly concise expression. To improve the computational efficiency, a fast algorithm for calculating the oil-film force and Jacobian of the local pad system is proposed and the Newton–Raphson method is used for solving the equilibrium positions of the journal and all pads. Taking a rigid rotor symmetrically supported on two identical five-shoe tilting-pad journal bearing as an example, the complete dynamic characteristics, damping natural frequency and the stability are calculated. Compared with the traditional reduced model, the numerical results show that the dynamic characteristics can be calculated efficiently and succinctly. The stability can also be overestimated by using the reduced model.     

Modeling lubricant flow between thrust-bearing pads

Inlet temperature is one of the main inputs in all models for the analysis of fluid film bearing performance. At the same time, inlet temperature distribution and also oil velocity distribution at the inlet are the result of flow phenomena in the gap between the bearing pads. These phenomena are complex and in many cases further affected by any special arrangements of forced oil supply to the gap between pads. The reason for such arrangements is the more efficient introduction of externally cooled lubricant. Not many details are known about any flow phenomena in the gap between the pads and even less if the bearing is fitted with any kind of directed lubrication system. Contemporary tools of computational fluid dynamics (CFD) enable one to study the flow between bearing pads and even to build models of a whole hydrodynamic bearing. Preliminary results of modeling lubricant flow in the gap, in a bearing with a direct oil supply system will be presented in this paper. The effects of modified inlet oil temperature on some aspects of bearing performance are also presented.     

Prevention of fluttering fatigue damage in a tilting pad journal bearing

Tilting pad journal bearings have been widely used to support high-pressure/fast rotating turbine rotors owing to their inherent dynamic stability characteristics. However, fatigue damage in the upper unloaded pads and the break of locking pins by pad fluttering continuously take place in actual steam turbines. The purpose of this paper is to develop a bearing model that can prevent bearing problems effectively using pad fluttering in a tilting pad journal bearing. A developed bearing model with a wedged groove is suggested from studies of a fluttering mechanism performed in previous research. The fluttering characteristics of the upper unloaded pad are studied experimentally in order to verify the reliability of the bearing model. It was found that very little pad fluttering nearly occurs in the bearing model under various experimental conditions. In addition, no type of bearing failures by pad fluttering was detected in applications involving actual steam turbines.     

Experimental study on the characteristics of pad fluttering in a tilting pad journal bearing

The fluttering characteristics of the upper unloaded pads in a tilting pad journal bearing were studied experimentally. In order to investigate the fluttering phenomena of the pad, the absolute vibration of the pad, the relative vibration between the bearing and the shaft, and the circumferential film thickness/film pressure were measured with the variation of the supply oil flow rate, the shaft speed, and bearing load. By analyzing the circumferential distributions of the film thickness, it was identified that the film shape of the upper pad continuously alternates between the wedge shape and the diverged shape in the rotational direction while the shaft is rotating. And it was discovered that the pads tend to a representative sub-synchronous self-excited vibration exactly like classical rotor-bearing instability, defined as the oil whirl and oil whip phenomena, with the increase of rotating speed from the cascade plot of the pad. The major finding was that the incipient fluttering velocity of the pad increased with the increase of the supply oil flow rate but decreased with the increase of the bearing load. The experimental results also showed that the fluttering amplitudes of the pad can be effectively suppressed by controlling the supply oil flow rate.     

对具有可倾瓦块和固定瓦块的混合型径向滑动轴承性能分析

本分析计算了顶部瓦块固定的可倾瓦径向滑动轴承（简称混合型轴承）的性能参数,与相同尺寸的可倾瓦径向滑动轴承相比,该种混合型轴承在承载能力,流量,摩擦功耗,平均温升等方面都发生了变化,具有明显的特点,最后的验测试验证了本所采用的分析计算方法是可行的。     

Tri-Conical Gap-Shaped Externally Pressurized Gas Bearing Pads

Externally pressurized gas (EPC) bearing pads with convergent conical shapes can provide high load capacity and high stiffness. Research has revealed that if the suitable combination of gap difference and working gap height is chosen, the optimized diameter ratios for stiffness and load capacity are close to the same value, about 0.8 to 0.9, or the ratio of the diameter of the conical gap-shaped part over the pad diameter. The optimized diameter ratio is independent of the supply pressure, the pad diameter and the number of conical parts. Conversely, the stability of the bearings is controlled by the combination of the diameter ratio and the gap difference. From the analysis of the stability criteria and the optimized diameter ratio, the concept of the tri-conical gap-shaped EPG bearing pads was proposed. Numerical and experimental investigation shows that under the same stable conditions, tri-conical gap-shaped pads provide higher stiffness and higher load capacity than simple conical or parallel gap-shaped pads.     

基于多物理场耦合的可倾瓦滑动轴承性能优化分析

针对大型可倾瓦滑动轴承的湍流效应和瓦块变形,基于COMSOL和MATLAB的联合仿真构建三维热弹流体动力润滑模型.模型中,考虑湍流的修正雷诺方程、能量方程和热传导方程的计算采用COMSOL偏微分方程物理场模块实现,瓦块变形计算采用COMSOL中热应力物理场模块实现,多物理场耦合和计算过程控制利用MATLAB实现.基于所...     

基于数值模拟的小孔节流空气静压轴承静动态特性研究

为了提高小孔节流空气静压轴承的静动态性能,基于流体力学和固体力学的基本控制方程,建立小孔节流空气静压轴承双向流固耦合数值模拟模型;采用静态数值模拟方法获取了设计参数对承载力和刚度的影响规律,进一步对微气膜间隙内三维流场特性进行了分析,有效降低了微气膜间隙内气体冗余现象对空气静压轴承动态稳定性的影响,并在数值计算的基础上对空气静压轴承结构和工作参数进行优化设计;在气体静压试验平台上对自行研制的空气静压轴承进行静动态特性测试。试验结果表明:所提出的数值模拟方法具有很好的预测效果;所采用的优化设计方法能够显著提升空气静压主轴的静动态特性。