液膜密封端面汽蚀机理及对密封性能影响研究

Cavitation of the face in non-contacting mechanical seals lubricated by liquid film includes macroscopic cavitation caused by waviness, taper, inclination, etc. of the face, and microscopic cavitation produced by surface roughness. Said cavitatiion significantly affects the stability and reliability of the seal. This project aims to expand comprehensively theoretical and experimental study on the said cavitation. In the project, the physical model considering waviness, taper, inclination and roughness of the seal face is established firstly; secondly, based on the generalized Reynolds equation considering cavitation, the steady state characteristic parameters, such as the distribution of the fluid film pressure and temperature, bearing capacity, fluid film stiffness, friction coefficient, and the dynamic characteristic parameters, such as stiffness coefficient, damping coefficient under small perturbation condition is analyzed using the finite element method; thirdly, a dynamics model of the "rotor - bearing - seal" system is developed to derive the motion equations under the conditions of small perturbation, and then, the change regulation of the dynamic stability and the condition of the steady state of the system is got by investigating the dynamic stability; fourthly, using the multi-functional sealing experimental device, the real-time measurement of the characteristic parameters of the fluid film, such as pressure, thickness, stiffness, etc. is realized, to study the characteristics of the fluid film and stability of the sealing system on the simulated cavitation conditions, then to verify or amend the theoretical research. The study will elucidate the mechanism of the mechanical seal cavitation and the influence on the sealing performance. Furthermore, the foundation will be laid for the improvement of the theory and method about the design of mechanical seals, and the development of late-model liquid film mechanical seals with independent intellectual property rights used in the condition of high parameters.

非接触式液膜密封端面汽蚀包括由端面波度、锥度、倾斜度等导致的宏观汽蚀和由表面粗糙度产生的微观汽蚀，显著影响密封的稳定性和可靠性。本项目拟对其开展深入的理论及实验研究，主要涉及建立包括端面波度、锥度、倾斜度以及表面粗糙度的物理模型，基于考虑汽蚀的广义雷诺方程，采用有限元法分析流体膜的压力温度分布、承载能力、刚度、摩擦系数等稳态特性，微扰条件下流体膜的刚度系数、阻尼系数等动态特性；建立"转子-轴承-密封"系统动力学模型，推导其微扰条件下的运动方程，进而探讨其动态稳定性，得出其变化规律及稳态判定条件；利用多功能密封实验装置实时测量端面流体膜压力、厚度、温度等特征量，模拟研究汽蚀条件下液膜密封的流体膜特性及密封系统的稳定性，对理论研究进行验证或修正。该研究必将阐明密封汽蚀机理及对密封性能的影响规律，为提升完善机械密封设计理论和方法，进而研发具有自主知识产权的新型高参数液膜密封奠定基础。

非接触式液膜密封端面的宏观汽蚀和微观汽蚀显著影响密封的稳定性和可靠性。本项目基于广义雷诺方程，结合质量守恒空化边界条件，建立了考虑表面形貌与形状误差的液体润滑机械密封数学模型，揭示了各因素对空化区域初生及其演变的影响规律，进一步分析了空化汽蚀条件下流体膜的压力分布、承载能力、流体膜刚度、泄漏率等稳态特性参数的变化趋势；基于空化发生机制提出了周向斜面台阶结构以降低密封端面间液体流动发散区液膜压力损失，探讨了不同槽深时，斜面转角比对液膜压力、降低空穴发生及流体动压性能的影响，实现了对液膜空化现象的抑制；采用小扰动法及有限元法，研究了微扰条件下密封平衡位置处流体膜的刚度系数、阻尼系数等动态特性参数，进而改变端面波度、锥度等影响密封端面汽蚀的因素，得到了各因素对流体膜动态特性的影响规律；建立了螺旋槽液膜密封涡动-空化模型以探究液膜空化导致密封性能变化对“转子—轴承—液膜密封”系统动态稳定性的影响，借助计算流体力学软件对涡动工况下的密封性能进行仿真模拟，对液膜空化现象与密封环涡动之间的影响关系进行了分析；最后，基于自主设计的可视化实验装置对下游泵送螺旋槽密封空化特征进行实验研究，实现了对空化区域的可视化观察，探讨了油压和转速对不同螺旋槽密封液膜中空穴发生位置、空穴分布及空穴边界的影响。研究从根本上揭示了密封汽蚀机理及对密封性能的影响规律，丰富完善了非接触式机械密封的设计理论和方法，为研制开发适用于不同工况要求的高性能非接触式密封技术奠定了理论基础。