柱面气膜密封动力特性系数的数值计算

针对柱面气膜密封系统动态特性分析问题,应用微扰线性化分布参数法建立密封气膜的微扰动态压力微分方程组,给出柱面气膜密封双自由度微扰下密封气膜的动态刚度和动态阻尼系数的计算方法;建立密封气膜的8个动态刚度、阻尼系数的有限元分析模型,给出有限元数值仿真计算流程和方法;通过算例验证数值计算模型和求解方法的正确性并重点研究可压缩数和平均膜厚对气膜动特性系数的影响.以柱面顺流螺旋槽带坝界面结构为例计算密封气膜各项动特性系数并给出不同条件下的变化规律曲线,气膜的正向刚度系数和正向阻尼系数呈现较为复杂变化状况,交叉刚度系数和交叉阻尼系数呈现轴对称特性.密封气膜动特性系数数值计算为稳定性分析提供了基础,为密封系统设计提供了指导.     

周向波度气体密封的动态特性

基于摄动法求解周向波度气体密封的动态Reynolds方程,得到动态气膜压力分布。计算周向波度气体密封的气膜动态刚度和阻尼系数,分析扰动频率及密封端面几何参数,如波数、波幅和坝宽比对气膜动态特性系数的影响规律。结果表明:当扰动频率小于转轴角速度时,其对气膜动态特性系数影响不大,反之有较大影响;波数对气膜动态特性系数影响不大,随着波幅的增加主刚度系数和阻尼系数都随之减小,耦合刚度系数则几乎不受影响,随着坝宽比的增加刚度系数基本保持不变,阻尼系数均增加。     

锥度及静态静环角偏差对低速干气密封气膜动态特性的影响

利用小扰动法结合有限元法求解气膜控制方程——动态雷诺方程,得到了端面稳态及动态压力分布.计算了表征气膜动态特性的主要参数——刚度系数和阻尼系数,分析了端面锥度和静态静环角偏差对气膜动态特性的影响规律.结果表明:负锥度对主气膜刚度系数和主阻尼系数有显著影响,正锥度影响较小;静态静环角偏差对主气膜刚度系数和主阻尼系数以及耦合气膜刚度系数和阻尼系数都具有明显的影响;通过调节密封端面锥度和角偏差可以改变气膜动力学行为,进而可以改善密封环的角向运动.     

计入JFO边界条件的波度机械密封动态特性分析

为研究微扰下的波度端面机械密封的动态特性,基于流体润滑理论和小扰动法,考虑液膜空化建立计入JFO边界条件的微扰膜压控制方程,数值求解密封端面液膜三自由度微扰下的动态刚度和阻尼系数,分析几何参数和操作参数对波度端面机械密封动态特性系数的影响规律。结果表明：随着介质压力的增大,液膜动态刚度和阻尼系数均增大,有利于提升密封动态稳定性;高转速下虽液膜动态刚度系数增大,但液膜阻尼特性变差,密封工况运行易产生失稳;随着波锥比的增大,液膜动态刚度和阻尼系数均增大;波数约为8、坝宽比约为025时,液膜动态刚度和阻尼系数能得到相对优化结果。     

柔性端面气膜密封流场分析及密封特性研究

提出一种航空发动机主轴承端适用密封——柔性端面气膜密封。通过对三种密封端面变形情况下的压力控制方程进行求解,获得密封气膜微尺度流场特性的演变规律,并探讨关键密封性能参数与工况条件的相关性。研究结果表明：柔性端面在带压气膜的作用下发生变形,其中波箔片的变形起主导作用,平箔片的影响可忽略不计;相较于刚性端面,柔性端面可有效增大气膜开启力,同时泄漏量也增大;在不同进出口压力比、转速以及初始气膜厚度下,二者部分密封特性呈现出不同的变化趋势,间隙楔形效应使柔性端面的黏性摩擦力矩和气膜刚度变化率均小于刚性端面的相应数值。通过研究结果推断,柔性端面结构可在高速低压工况下具有更稳定的综合密封性能。     

基于热气弹耦合的悬臂式箔片气体动压轴承动态特性分析

在考虑气膜与弹性箔片的耦合作用,以及可压缩动压流体热效应和热传导影响的基础上,建立了悬臂式箔片气体动压轴承热气弹耦合性能计算模型,并据此分析了箔片数目、长径比和偏心率对轴承动态特性的影响。研究结果表明:随着箔片数目的增加和长径比的增大,轴承刚度系数和阻尼系数逐渐增加;在大偏心率下,箔片会产生较大变形并调整气膜厚度,故轴承刚度系数有所下降。因此,对于悬臂式箔片气体动压轴承支承的转子系统而言,可通过优化轴承箔片数目、厚度、长径比等结构参数提升系统动态性能及稳定性。     

环形微槽浮动密封的动态特性分析

基于高参数旋转装备对密封低泄漏和长稳定的苛刻要求，提出一种环形微槽浮动密封；考虑偏心气膜收敛问题，定义了Rayleigh台阶对气膜周期的突变性，并应用小扰动法建立瞬态Reynold方程，获得压力和膜厚的扰动微量关系式；构建动态刚度与动态阻尼矩阵，并研究槽型结构与工况对动态特性系数的影响。研究结果表明：交叉刚度kxy和kyx的曲线与交叉阻尼cxy和cyx的曲线分别呈现对称性，主刚度kxx和kyy、主阻尼cxx和cyy的变化规律保持一致；在-20°与30°螺旋角下主刚度达到了最大值；在槽数为10时主刚度、主阻尼达到了最大值，同时交叉刚度之差与交叉阻尼之和趋于0，说明槽数为10时利于密封稳定；在转速超过38 000 r/min后密封系统有可能发生不稳定；压差对密封压力流和剪切流有明显的影响，使得密封系统处于涡动发散阶段；在大偏心下，楔形效应的增强抵抗了气膜压力与厚度分布的不均匀性，有利于涡动收敛，然而气膜厚度的增大增加了密封不稳定性的概率，从而推断出环形微槽浮动密封更适应于小膜厚、低压、高速、大偏心的服役工况。     

气体多孔端面机械密封孔径尺寸对密封动态性能影响研究

建立了气体润滑微孔端面机械密封(LST-MS)的气膜压力控制方程及雷诺方程,利用有限差分法和小扰动法计算了气膜稳态和动态压力分布,分析研究了频率数、面积比和布孔方式等参数对密封动态刚度和阻尼等表征气膜特性参数的影响.结果表明,高频扰动易使密封产生气膜振荡而导致密封失稳;孔径尺寸对密封气膜影响明显,随微孔列数的增多,刚度和阻尼均将逐渐趋于某一稳定值,频率数越大,则稳定值对应的微孔列数越多.     

气膜端面密封角向摆动自振稳定性

提出造成气膜端面密封角向摆动自振的内在机理，既有半频摆动自振又有角向气锤自振。在其稳定性分析中给出了不同端面结构、浮环支撑弹簧和二次密封阻尼等的影响。分析按照小扰动线性化的分布参数法，联立气膜微扰雷诺方程和浮环微扰运动方程，对密封系统的角向摆动自振稳定性界限进行了数值迭代。     

反转轴间气膜密封的结构参数与密封性能分析

对一种反转轴间双向气膜密封结构进行了研究,分析了其工作原理和系统平衡求解的过程.对密封结构与系统平衡位置的气膜支反力、气膜刚度及气体泄漏量之间的关系进行了分析对比.结果表明:密封腔内、外坝宽度增大,均使对应端面密封腔内腔宽度减小,密封腔气膜支反力下降,刚度下降,气膜厚度减小;主密封环B腔端面结构参数对系统整体密封性能影响较大,而C腔端面结构参数只对C腔端面气膜密封性能有影响.     

螺旋槽气体轴承动态特性及失稳分析

针对高速动静压气体轴承气膜的复杂非线性动力学行为,以球面螺旋槽动静压气体轴承为研究对象,建立润滑分析数学模型;采用有限差分法与导数积分法进行求解,得到动态扰动压力分布及动态特性系数,并研究切向供气条件下螺旋槽参数、径向偏心率、供气压力、转速对气膜刚度阻尼系数的影响规律;建立线性稳定性计算模型,预测气膜涡动失稳转速,分析运行参数对失稳转速的影响。结果表明:气膜阻尼是一种抑制涡动的因素,气膜的稳定性取决于气膜刚度与阻尼的协同作用;气膜刚度阻尼随着槽宽比、槽深比、螺旋角的增大,整体上呈先增大后减小的趋势;刚度随转速的升高而增大,阻尼则随转速的升高而减小;径向偏心率和供气压力越大,气膜刚度和阻尼越大;在一定范围内,提高供气压力、增大径向偏心率能够提高系统失稳转速;合理地选取轴承结构参数和运行参数,能够优化轴承动态特性,保证气体轴承较高的运行稳定性。     

Parametric Study of Spiral Groove Gas Face Seals

A finite element analysis for the isothermal flow in spiral groove gas face seals is detailed along with a successive approximation method for the iterative solution of the nonlinear Reynolds equation. Zeroth- and first-order pressure fields are calculated for evaluation of the seal opening force and leakage and the axial stiffness and damping force coefficients, respectively. A parametric study shows the static and dynamic force behavior of a baseline SGFS operating with a large pressure ratio. The recommended geometric parameters presented ensure large static stiffness and damping force coefficients while still allowing for low seal leakage rates. A reduction in the power loss and a significant increase in the seal static stiffness coefficient are unique features of thin seal dams.     

Structural Stiffness and Coulomb Damping in Compliant Foil Journal Bearings: Theoretical Considerations

Compliant foil bearings operate on either gas or liquid, which makes them very attractive for use in extreme environments such as in high-temperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing, which is time-consuming and expensive. In this paper, the authors present a theoretical model to predict the structural stiffness and damping coefficients of the bump foil strip in a journal bearing or damper. Stiffness is calculated based on the perturbation of the journal center with respect to its static equilibrium position. The equivalent viscous damping coefficients are determined based on the area of a closed hysteresis loop of the journal center motion. The authors found, theoretically, that the energy dissipated from this loop was mostly contributed by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonlinear behavior of the bump foil strips were examined. With the introduction of this enhanced model, the analytical tools are now available for the design of compliant foil bearings.     

基于波纹箔片刚度试验的气体箔片轴承动力学特性

为了研究波纹刚度特性以及其对箔片轴承动力学特性的影响,设计了波纹箔片刚度测试试验台。分别对两端固定和一端固定一端自由两种约束条件下的波纹箔片刚度进行了测试,并将试验结果与仿真结果进行了对比分析。最后基于轴承波纹结构刚度特性,利用小扰动法求解了轴承动力学特性系数,研究了波纹箔片刚度特性对轴承动力学特性系数的影响。结果表明：两端固定波纹箔片刚度较一端固定一端自由波纹箔片单位宽度刚度大5倍以上,并且随着波纹变形量的增加,两端固定约束使其波纹箔片刚度比一端固定一端自由波纹箔片更具有非线性,而刚度仿真结果并没有体现出非线性,只是模型中引入的结构摩擦因数使得刚度值随摩擦因数有所增大。最后轴承载荷增加会使得轴承刚度系数以及主阻尼增加,其他阻尼系数减小,并且鉴于波纹箔片刚度非线性的原因,采用刚度试验值计算得到的轴承动力学系数增加幅度要明显大于文献仿真模型。     

Minimum Film Thickness in a Gas Foil Journal Bearing with an Unbalanced Rotor

A gas-lubricated foil journal bearing consists of a compliant metal shell structure that supports a rigid journal or rotor by means of a gas film. The response of this system to the periodic forces of an unbalanced rotor supported by a single bearing is predicted using perturbation analysis. The foil structure and the gas film are modeled with an analytically perturbed finite element approach to predict the rotor dynamic coefficients. A dynamic model of the rotor is used to predict periodic journal motion. The perturbation analysis is then used with the periodic response of the rotor to calculate periodic changes in the gas film thickness. Other quantities such as the gas film pressure and the foil deflection can also be calculated. The model includes bending and membrane effects in the top foil, coupled radial and circumferential deflections in the corrugated sub-foil, and the equivalent viscous dissipation of Coulomb friction effects in the foil structure. The approach is used to investigate the effects of top-foil thickness on minimum film thickness in a bearing.     

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.     

Performance of a Complaint Foil Seal in a Small Gas Turbine Engine Simulator Employing a Hybrid Foil/Ball Bearing Support System

Operation of a non-contact compliant gas foil seal (CFS) in a high temperature hybrid dynamic simulator representative of a small gas turbine engine spool is discussed. At the hot section of the simulator two oil-free components, a CFS and a compliant foil bearing (CFB) were mounted and at the cold (compressor) section of the simulator, an oil-mist lubricated ball bearing was installed. The preliminary numerical study on the fluid flow and thermal analysis of a CFS was discussed in the previous work by the authors. The experimental results for successful operation of the foil bearing and foil seal at temperatures up to 560 °C and speeds up to 55,000 rpm are presented. The surface of the CFS and CFB journals for high temperature tests were coated with PS304 solid lubricant film, developed by NASA The CFS performance at different operating speeds and temperatures and differential pressures was investigated. In a similar test, a leakage flow comparison was made among a labyrinth seal, a brush seal and a CFS. The experimental results indicate superior performance of the CFS over the two other types of seals. Unlike brush seal, CFS showed no evidence of rub or induced wear on the journal or seal surface.     

ANALYSIS OF COUPLING INFLUENCES OF LABYRINTH SEAL PARAMETERS ON CROSS COUPLED STIFFNESS AND DIRECT DAMPING COEFFICIENT

A~ndal area Of cODtIDI volume (Inlnz )b~Breadth Of tOP of teeth(rnm)C, c--Damping (N' slm)e--Eccentricity~force(N)fi,fz--Coefficient of inchon factorC, X, Y--Constantsh~Height of teeth (mzn)K, k--S~s (N/m)L~ length Of seal cavihes (mxn)Li~Pitch (nun).m--~ mass flow (kg' m- 1' s- I )Nc--N~ Of seal cavihesnl --Circular speed Of ~ (r/ndn)nZ--ROtor speed (rlndn)p~Dess~ (Pa)p,--Dessme ~nce (Pa)R~Gas constant (J' kg~ l' K~ I )R,~ndus Of contIDI VOlume 1 (nun)RZ~ndus Of contIDI…