【作者】 张希；

【导师】 李富才；

【作者基本信息】 上海交通大学 ， 机械工程， 2016， 硕士

【摘要】 大涵道比涡扇发动机具有推进效率高、巡航油耗低、可靠性高等优点,广泛用作运输机和民航客机的主要动力装置。低压转子系统是涡扇发动机的关键组成部分,其结构复杂,尺寸受限于高压转子的装配,所以结构细长,支承跨度大,再加上工作时易受气动载荷、机动载荷、离心载荷和温度载荷的影响,造成了转子系统的振动问题突出。低压转子系统的结构强度分析是发动机整机设计的关键环节,建立有效的低压转子系统动力学分析模型是整机动力学研究的基础。涡扇发动机运转过程中,外物撞击或金属疲劳都有可能引发叶片的局部断裂,甚至造成整个叶身飞出,以致引发机毁人亡的严重空难。当叶片脱离发动机后,不平衡载荷可能会引起风扇转子的弯曲振动或扭转振动,甚至可能激发发动机绕挂架振动,诱发挂架低阶扭转振动,造成挂架的失效和破坏,导致发动机从飞机机翼上脱落,严重影响飞机的安全航行。同时,低压转子本身在高转速下承受较大的扭转力矩,轴系容易受到外界扰动而产生弹性振动或塑性变形,叶片脱落引入的不平衡载荷容易诱发转子系统的扭转振动。扭转振动现象具有潜伏性和突发性,在发动机运行状态下进行振动监测时往往不容易被发现,切向交变扭转应力引发材料产生疲劳积累,累积效应到达一定程度后,裂纹不断扩散,甚至引起材料断裂,严重影响发动机工作的可靠性与安全性。针对涡扇发动机低压转子系统,重点研究结构系统的振动特性及恶劣载荷下的动力学响应特性。本论文主要研究内容包括以下三个方面:第一,建立低压转子的有限元模型,进行风扇叶片和转子系统的预应力模态分析,着重关注恶劣载荷影响下低压转子的动力学响应特性,建立低压转子系统叶片脱落的有限元模型以及转子在不平衡载荷作用下的运动微分方程,进行有限元分析与数值求解结果对比。第二,研究低压转子系统扭转振动特性,建立转子非线性扭转振动的运动微分方程,对扭转振动中存在刚度渐软Duffing非线性现象的原因进行理论推导,并进行了转子结构的有限元仿真和扫频试验。第三,设计以转子扭转振动为基础的试验台,用于检验扭转振动理论分析过程和有限元仿真结果,并在此基础上提出涡扇发动机低压模拟转子叶片脱落试验台的台架总体设计方案。更多还原

【Abstract】 High bypass ratio turbofan engine which has the advantages of high propulsive efficiency,low cruise fuel consumption,high reliability is widely used as the main power plant of the aircraft.Low-pressure rotor system is a key component of a turbofan engine,and its structure is fairly complex.The size is limited by high-pressure rotor assembly structure,low-pressure rotor with slender structure and large bearing span works under aerodynamic,motor,centrifugal and temperature loads,so the rotor vibration problem is prominent.The structured analysis of the low-pressure rotor is one of the most important links in the engine design,and it is the foundation of the whole dynamics research to establish the effective low-pressure rotor system dynamics model.Due to foreign object impact or fatigue crack,partial even the whole blade will fly out,it will lead to engine accident,and even cause air crash.After fan blade out(FBO),unbalance load may cause the rotor bending vibration or torsional vibration,induce torsional vibration of pylons that can cause the failure of the pylons,even lead to the results that the engine fall from wings and it will cause serious effects on the safety of aircraft.Meanwhile,the low-pressure rotor is under large torque at high speed,shaft is vulnerable to external disturbances and produce elastic vibration or plastic deformation,unbalanced load causes the rotor system torsional vibration.The phenomenon of torsional vibration is latent and unexpected,vibration monitoring are often not easy to find,however,tangentially alternating torsional stress induces material fatigue accumulation,after the cumulative effect reaches a certain level,cracks continue to spread,the torsional vibration even cause fracture failure,which seriously affects the reliability and safety of the engine.Aiming at turbofan engine low-pressure rotor system,this thesis focuses on the vibration characteristics of the structure and dynamics response of the system under severe load.The main contents include three parts as follows:Firstly,a finite element model of low-pressure rotor is established to conduct pre-stressed modal analysis,the research focuses on the dynamics response under FBO unbalanced load,creates low-pressure rotor FBO finite element model and the differential equations of the rotor under unbalanced load,and makes the comparison of finite element analysis and numerical solution results.Secondly,this thesis researches on low-pressure rotor system torsional vibration characteristics,and creates the rotor nonlinear torsional vibration differential equations.At the same time,develops the theoretical derivation of the reasons for the existence of the Duffing nonlinear phenomenon in torsional vibration,finite element simulation and sweep frequency test of rotor is carried out.Thirdly,a test bench based on torsional vibration is designed to verify theoretical analysis results,the test bench would be used not only in the rubbing,unbalanced test,but rotor fault simulation and vibration test.What’s more,based on the design of torsional test bench,an overall scheme of the turbofan engine low-pressure simulated rotor FBO test bench was proposed.更多还原