超临界二氧化碳多槽型干气密封泄漏流动与动力特性研究

Leakage Flow and Dynamic Characteristics of Supercritical Carbon Dioxide Dry Gas Seals with Different Types of Grooves

关键词:  涡轮  压气机  泄漏流动  动网格技术  干气密封  动力特性  简谐微扰动

Key words:  Turbine  Compressor  Leakage flow  Dynamic mesh technology  Dry gas seal  Dynamic characteristics  Microscale perturbation

摘要:

针对超临界二氧化碳（SCO₂）旋转机械面临的严重泄漏、气流激振引发转子失稳等问题，以美国通用电气公司10MWe SCO₂循环中高压涡轮的轴端密封为研究对象，设计了螺旋角15°和30°的螺旋槽、T型槽和ST型槽的四种槽型结构的干气密封。采用基于动网格技术和非定常CFD数值方法的微尺度摄动模型，研究了在实验边界条件下干气密封的稳态性能及在轴向简谐微扰动下SCO₂涡轮轴端干气密封的非稳态动力学特性。对比分析了3种动压槽深度、2种动压槽角度下的干气密封泄漏量、静态气膜刚度、动态气膜刚度和阻尼系数。研究表明：四种槽型均满足泄漏流量的设计要求。随着动压槽深度的增加，干气密封开启力与泄漏流量均增大。ST型槽干气密封有着较大的气膜刚度和刚漏比，同时其在面对轴向微尺度摄动时最为稳定，是综合性能最优秀的干气密封结构。

Abstract:

By aiming at the serious leakage and rotor instability problem caused by the perturbation of fluid flow in supercritical carbon dioxide （SCO₂） rotating machines， four kinds of dry gas seals with spiral groove， T groove and ST groove with spiral angle 15° and 30° are designed. The 10MWe SCO₂ Brayton cycle designed by GE company is chosen as the research subject. A micro-scale perturbation model based on the transformation mesh technique and unsteady CFD numerical method is used to study both the steady and unsteady dynamic characteristics of the dry gas seal at the shaft end of the SCO₂ turbine under the experimental boundary conditions. The leakage flow， static film stiffness， dynamic film stiffness and damping coefficient under 3 groove thicknesses and two groove angles are compared and analyzed. The results show that the four kinds of dry gas seals all meet the design requirements of limit leakage flow. With the increase of the groove thickness， both the leakage flow and the opening force of the dry gas seal increase. ST groove dry gas seal has the relatively large film stiffness and stiffness-leakage ratio. Besides， it’s the most stable one when facing the axial microscale perturbation. Thus， the ST groove dry gas seal is comprehensively the best dry gas seal among the four.