Reliability estimation of mechanical seals based on bivariate dependence analysis and considering model uncertainty

The reliability estimation of mechanical seals is of crucial importance due to their wide applications in pumps in various mechanical systems. Failure of mechanical seals might cause leakage, and might lead to system failure and other relevant consequences. In this study, the reliability estimation for mechanical seals based on bivariate dependence analysis and considering model uncertainty is proposed. The friction torque and leakage rate are two degradation performance indicators of mechanical seals that can be described by the Wiener process, Gamma process, and inverse Gaussian process. The dependence between the two indicators can be described by different copula functions. Then the model uncertainty is considered in the reliability estimation using the Bayesian Model Average (BMA) method, while the unknown parameters in the model are estimated by Bayesian Markov Chain Monte Carlo (MCMC) method. A numerical simulation study and fatigue crack study are conducted to demonstrate the effectiveness of the BMA method to capture model uncertainty. A degradation test of mechanical seals is conducted to verify the proposed model. The optimal stochastic process models for two performance indicators and copula function are determined based on the degradation data. The results show the necessity of using the BMA method in degradation modeling.     

Dynamic performance of a C/C composite finger seal in a tilting mode

The complex operating state of aeroengines has an impact on the performance of finger seals.However,little work has been focused on the issue and the dynamic performance of finger seals is also rarely studied.Therefore,a distributed mass equivalent model considering working conditions is proposed in this paper for solving the existing problems.The effects of the fiber bundle density and the preparation direction of the fiber bundle of a C/C composite on the dynamic performance of a finger seal are investigated in rotor tilt based on the proposed model.The difference between the C/C composite finger seal performances under the rotor precession and nutation tilt cases is also investigated.The results show that the fiber bundle density and the preparation direction of the fiber bundle have an influence on the dynamic performance of the finger seal as rotor tilt is considered,and the dynamic performance of the finger seal is different in the two kinds of tilting modes.In addition,a novel method for design of finger seals is presented based on the contact pressure between finger boots and the rotor.Finger seals with good leakage rates and low wear can be acquired in this method.     

Effects of tooth bending damage on the leakage performance and rotordynamic coefficients of labyrinth seals

Tooth bending damage resulting from an intense impact by the rotor sometimes occurs in the transient operation. To investigate the influence of after-damage clearance and tooth bending length on the leakage performance and rotordynamic coefficients of labyrinth seals, three tooth bending damages were taken into consideration, including the unbent tooth damage (abbreviated as Unbent), the partial tooth bending damage (abbreviated as Pbent) and the complete tooth bending damage (abbreviated as Cbent). The transient CFD solution was utilized to calculate the leakage flow rates and rotordynamic coefficients of labyrinth seals with clearances of 0.3, 0.4, 0.5, 0.6 mm for three tooth bending damages. The obtained result shows that the Unbent tooth damage leaks least while the Pbent tooth bending damage leaks most, and an increase of 6.1% for Cbent tooth bending damage and an increase of 19.4% for Pbent tooth bending damage are discovered at the tooth clearance of 0.6 mm in comparison with the Unbent tooth damage. Compared to the Unbent tooth damage, the effective damping for Pbent tooth bending damage and Cbent tooth bending damage is lower and drops by 9.7%–33.6% and 8.5%–22.6% respectively at the tooth clearance of 0.6 mm, suggesting that Pbent tooth bending damage or Cbent tooth bending damage tends to weaken the seal stability when compared to the Unbent tooth damage.     

封严涂层的性能评价及研究进展

封严涂层系统可以改善飞机燃气涡轮发动机中旋转部件和固定部件之间的密封性,已成为提高发动机工作效率．延长发动机服役寿命的主要方法之一。本文阐述了目前封严涂层的应用及性能评价的研究进展．描述了未来封严涂层的发展趋势。     

涡轮径向轮缘密封非定常燃气入侵和封严效率的数值研究

为防止燃气入侵涡轮盘腔,提高运行安全性,对盘腔和轮缘密封间隙内非定常流动机理进行了深入研究。采用数值求解三维URANS（Unsteady Reynolds Averaged Navier-Stokes）和SST湍流模型的方法,研究了涡轮径向轮缘密封的非定常燃气入侵和封严效率。数值计算的径向轮缘密封的封严效率和环量比与实验数据吻合一致,验证了数值方法的可靠性。分析了6种冷气流量下径向轮缘密封的非定常压力分布、封严效率和燃气入侵与冷气出流特性。研究表明：冷气流量的增加阻止了径向轮缘密封处的燃气入侵和强化了冷气出流,径向轮缘密封盘腔内的封严效率随着冷气流量的增加而增加;动盘附近的封严效率高于静盘;入侵燃气基本被限制在径向轮缘密封的间隙区域。径向轮缘密封间隙出口处的主流周向时均压力随着冷气流量的增加而增加,周向时均压力最大值与最小值的差值随着冷气流量的增加而减小。当动叶前缘与静叶尾缘距离较近且不断靠近的过程,主流周向压力最大值与最小值的差值增大,动静叶相分离的过程周向压力最大值和最小值的差值减小。在静叶和动叶间非定常干涉作用下,轮缘密封间隙出口区域主流周向压力最大值与最小值差值较大时刻的主流低压区域具有优良的封严效率,同时高压区域的燃气入侵导致封严效率降低。     

聚硫橡胶研制与工艺方法的研究

介绍了聚硫橡胶配方的选择、技术性能的测试、工艺方法的确定和要求，以及在使用中应注意的几个问题。该胶已在航天产品的红外光学系统和电子电气系统中得到应用。应用表明，该胶性能稳定，质量可靠。     

耐海洋环境腐蚀的航空发动机封严涂层技术及其发展

对耐海洋腐蚀热喷涂可磨耗封严涂层在航空发动机领域的应用进行了论述,重点介绍航空发动机用热喷涂涂层的海洋气氛电化学腐蚀机理及相应涂层结构与材料设计等防护方法,提出了未来航空发动机用耐海洋腐蚀热喷涂封严涂层的发展方向.     

几何参数对刷式密封泄漏和刷丝尖端力的影响

建立了一种刷式密封的切片式三维模型,利用计算流体动力学(CFD)方法,计算了刷丝所受的气流力并将其简化为较少量的一系列的集中力.基于力矩平衡和线性叠加原理,提出了气流力引起的刷丝尖端力、转矩的一种定量计算方法.1台刷式密封实验台和1只实验刷环被用于相关理论计算 的实验验证.基于上述理论计算,利用正交实验研究了刷丝长度、刷丝间隙、刷丝排数、安装角、刷丝直径和保护间隙对泄漏率、气流力、刷丝尖端力和转矩的影响.结果表明,总泄漏率及转矩的计算与实验结果基本吻合,各点误差均小于20%.刷丝直径、刷丝间隙、保护间隙及刷丝排数的对总泄漏率影响非常显著,安装角对转矩的影响非常显著.      

浮环密封泄漏特性数值计算与试验

为了研究不同压差、温度和转速下浮环密封的泄漏特性,建立了CFD数值计算模型,计算分析了某型航空发动机浮环密封泄漏特性。针对转速引起的泄漏量变化,提出了通过有限元方法计算不同转速下密封跑道的离心膨胀量对流场尺寸进行更改;针对温度、压差引起的流体状态参数改变,通过状态方程进行计算,并对本构方程中相关参数进行重新确定。为有效验证数值计算模型的有效性,进行了全工况条件下浮环密封泄漏特性试验。结果表明:随着压差升高,数值计算得到的泄漏量不断趋近试验结果,在压差大于等于0.1 MPa后,数值计算得到的泄漏量与试验结果的平均偏差在6.08%~9.43%。     

有无蜂窝的直通斜齿流动特性旋转实验研究

为了研究蜂窝对直通斜齿流动特性的影响,在光滑衬套和蜂窝衬套条件下的高速旋转篦齿实验台上,分别测量了工作间隙和流动特性随转速0～8700r/min和压比1.1～1.5的变化规律。实验结果表明:随着转速的增加,泄漏量下降了约50%,流量系数下降了约25%,风阻温升达到40K;随着压比的增加,泄漏量和流量系数也相应增加;蜂窝衬套相对于光滑衬套,流量下降了约20%,流量系数下降了约10%,风阻温升差异微小。蜂窝可以使篦齿流量及流量系数降低,提升封严性能,对风阻温升影响很小。