【作者】 王强；

【导师】 吉洪湖；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2020， 博士

【摘要】 随着航空发动机综合性能的不断提高,其热力参数不断增大,导致密封工作条件也越发苛刻,传统的篦齿和石墨等密封技术已渐渐无法满足密封要求。指尖密封是一种具有广泛应用前景的柔性密封技术,可承担叶片叶尖、压气机和涡轮级间以及轴承腔等部位的密封任务,具有低泄漏、低成本等特点。然而,由于指尖密封通常为接触式密封,且其往往工作在高温、高压差和高转速的环境中,使得其面临着复杂的磨损、摩擦生热、泄漏流动、传热和热变形等问题。在此背景下,本文针对基本型指尖密封结构的上述问题开展了理论分析、数值模拟与试验研究工作。在模型建立方面,首先,基于能量守恒理论,在考虑摩擦与磨损相互耦合影响的前提下,分别建立了指尖密封与转子表面摩擦副双向磨损模型与摩擦生热模型。上述模型综合考虑了结构、工况与材料物性参数等多因素的影响,并提出了模型中摩擦、磨损系数、接触力修正系数以及磨损耗能比例等参数的试验确定方法。其次,建立了考虑摩擦磨损的指尖密封泄漏流动与传热各向异性多孔介质模型,该模型基于多孔介质理论,综合考虑了流动阻力系数与导热系数张量在空间上的各向异性分布以及由磨损引起的指单元变形所导致的上述参数随时间的变化。最后,发展了流动传热与热变形数值计算方法并采用典型密封结构的试验数据对上述计算模型进行了修正与验证,试验表明计算模型的误差大都在10%以内。在试验研究方面,首先建立了一套可用于多种形式密封泄漏、传热、摩擦阻力和磨损性能测试的高温高速试验系统。该系统具有如下特点:能够针对多种尺寸,特别是大尺寸密封结构进行性能测试;密封上下游气流均匀稳定、装配精度高、拆装方便;可以进行包括转轴扭矩与密封表面温度等在内的多种类、多测点参数测量。其次,提出了薄板原材料整平、整环慢走丝线切割以及高精度定位销组装等指尖密封加工工艺,试验结果表明本文的指尖密封试验件较同类型的密封结构具有优异的密封特性。最后,设计、加工了八种结构的指尖密封件并对其进行了流动传热与摩擦磨损性能测试。结果表明:密封泄漏量随着压差的增大而增大,随着来流温度的升高而减小,在转速上升阶段随着转子表面线速度的增大呈现出先减小后增大的趋势,但在下降阶段出现明显的滞后效应,且转子表面最高线速度的值越大其在降速过程中的滞后也越严重;密封与转子接触表面最高温度在转速上升阶段随着转子表面线速度的增大而增大,但在转速下降阶段由于滞后效应的产生其温度同样出现了滞后现象;随着磨损的发生密封与转子接触表面温升越来越小但泄漏量越来越大,且磨损量、温升与泄漏量的剧烈变化均发生在磨损初期;密封引起的摩擦扭矩与转子表面线速度呈正比,且随着密封上下游压差的增大而增大。在指尖密封性能的数值模拟方面,基于正交实验设计方法设计了算例方案并对典型密封结构的压力、速度和温度分布进行了模拟并分析了结构参数和磨损效应对泄漏与传热特性的影响规律。结果表明:转子表面线速度和初始安装过盈量越大,最终的径向磨损长度与磨损速率以及初始的摩擦生热量及其衰减速率也越大;磨损对泄漏与传热影响的数值计算结果与试验得到的规律一致;密封的压降主要发生在后挡板保护高度以下区域,且流体主要也是通过指梁下部和指尖靴区域泄漏的;密封最高温度出现在指尖靴与转子接触表面的略下游处,从此处开始温度沿径向和轴向降低,但温度的径向变化更为显著;此外,利用正交实验设计方法分析可知,综合考虑结构参数对磨损、摩擦生热、泄漏流动与传热特性的影响时,建议结构参数指梁圆弧圆心所在圆直径和指尖靴上端部直径选取较大值;热变形计算结果表明沿周向的热变形最大。更多还原

【Abstract】 With the improvement of the comprehensive performance of the aero engine,the thermal parameters are increasing,resulting in severe working conditions of the seals.The traditional sealing techniques such as labyrinth and carbon seals have failed to meet these requirements.Finger seal is a new type of compliant seal configuration,which is used to control leakage throughout the blade tip,compressor and turbine stage,bearing and disk cavities of an aero-engine or its accessory systems.It has superior sealing performance compared with labyrinth seals and a lower manufacturing cost than brush seals.However,the high-temperature,high-pressure difference and high-speed working conditions coupled with the structure characteristics lead to complex wear,friction heat,leakage flow,heat transfer and thermal deformation characteristics of finger seals,especially for contacting type.Thus,the above characteristics of basic finger seal are studied in this paper by using theoretical analysis,numerical simulation and experimental research.In terms of model establishment,firstly,a bilateral wear model and a friction heat model were established on the basis of energy conservation theory,respectively.In these models,the effect of structural parameters,working conditions and material properties are considered.Then,the experimental methods for determining the friction coefficient,wear coefficient,correction coefficient of contact force and ratio of wear energy to friction power were proposed.Secondly,an anisotropic porous media model for leakage flow and heat transfer analysis of finger seals was established,while the friction and wear effect were considered.The model considers the spatially anisotropic distribution of the flow resistance coefficient and thermal conductivity tensor,and the variation of the above parameters with time caused by deformation and wear of fingers.Finally,the numerical analysis methods of fluid flow,heat transfer and thermal deformation wre developed and the experimental data of typical finger seals were used to verify the calculation accuracy of the calculation models,test results prove that the accuracy of the modified models are mostly within 10%.In terms of experimental research,firstly,a high-temperature,high-speed seal test system was established which can be used to test the leakage,heat transfer,friction resistance and wear performance of various seals.The advangtages of this test system are as follow: it can test the sealing performance of a variety of sizes,especially for large-scale seal structure;upstream and downstream air flow is stable;it is easy to disassemble and assemble with high accuracy;many kinds of parameters including torque of shaft and surface temperature of seal can be measured.Secondly,the author proposed the processing technology of finger seal include the sheet material flattening,the whole ring tardily wireelectrode cutting and high precision dowel assembly.The results show that the finger seal designed in this paper has superior sealing performance compared with the same type of seal structures.Finally,designing and manufacturing eight kinds of finger seals and test their friction,wear,leakage and heat transfer performance.The results show that the leakage increases with the increase of pressure difference,but decreases with the increase of fluid temperature;the leakage initial decreases and then increases with the surface velocity in the rising stage,but there is obvious hysteresis effect in the descending stage,and the higher the maximum value of surface velocity,the more serious the hysteresis effect;the highest temperature of the seal increases with the surface velocity in the rising stage but also shows hysteresis in the descending stage;the temperature of the contact surface decreases but the leakage increases with the wear time,and the drastic changes of wear,temperature rise and leakage all occurred in the initial wear stage;the friction torque caused by the seal is proportional to the surface velocity of the rotor and increases with the increase of pressure difference.In terms of numerical simulation of performance of finger seal,the example scheme was designed based on the orthogonal test design method and the pressure,velocity and temperature distribution of typically finger seal were numerically simulated,and the influence of structural parameters and wear effect on leakage and heat transfer characteristics were analyzed respectively.The results show that the larger the rotor surface velocity and initial installation interference,the larger the final radial wear length,the wear rate,the initial friction heat flux and its decay rate;the numerical results of the effect of wear on leakage and heat transfer are consistent with the experimental data;most of the fluid leaks through the finger foot while the pressure drops mainly in this field;the highest temperature occurs at the downstream side of the contact surface between the finger foot and the rotor,and then the temperature decreases in the radial and axial direction,but more significant in the radial direction;In addition,by using the orthogonal test design method,it is suggested a large value of the diameter of finger foot upper and finger beam arcs’ centres,while synthetically considering the effect of structural parameters on wear,friction heat,leakage flow and heat transfer characteristics;it is found that the circumferential thermal deformation is the largest.更多还原