Nonlinear vibration of multi-spool aero-engine assemblies

大多数现代喷气发动机是多转子组件，包括两个或三个同轴嵌套转子，以不同的、模糊相关的速度旋转。这种系统的振动特性相当复杂，这是由于与轴承一起使用的油膜阻尼器（挤压油膜阻尼器-SFD）将所谓的非线性引入到组件中。将这种非线性元件设计到组件中呈现出棘手的问题，这是由于潜在的不期望的影响，如发动机的加速和减速上的振幅跳跃，以及与旋转速度不同步的振动。预测和分析此类现象的能力对于保证发动机和机身的结构完整性、发动机平稳运行和降低噪音水平至关重要。目前还没有有效的计算方法，这样做的多转子发动机在可行的时间范围内，因此，这种系统的非线性动力学知之甚少。实际上，运行振动测量经常揭示的现象，不能预测的个别非线性阻尼转子孤立考虑目前的分析研究。拟议的项目涉及创建一个工具，用于多转子航空发动机组件的非线性振动的有效预测，并通过使用这种系统的分析。拟议项目的目标是：（i）设计一种计算工具，显着增强当前转子动力学建模平台的能力;（ii）在非线性动力学理论的背景下研究航空发动机组件的振动特性; ㈢建造一个双轴发动机简化模型试验台，作为非线性振动现象的实验室演示器;（iv）为将SFD设计到典型航空发动机组件中的合理方法制定指导方针。该研究计划将把基础研究与非线性动力学理论结合起来，并进行更多涉及计算建模和实验验证的应用研究。这项研究的结果将主要有利于航空航天工业，在其寻求开发更轻，更有效的发动机设计，同时跟上越来越严格的安全要求。

Most modern jet engines are multi-spool assemblies comprising two or three co-axial nested rotors rotating at different, ambiguously related speeds. The vibration characteristics of such systems are considerably complex due to the so-called nonlinearity introduced into the assembly by the oil film dampers ( Squeeze Film Dampers - SFDs) used with the bearings. Designing such nonlinear elements into the assembly presents a tricky problem due to potential undesirable effects like amplitude jumps on acceleration and deceleration of the engine, and vibration that is not synchronous with the rotational speeds. The ability to predict and analyse such phenomena is essential to guarantee structural integrity of both engine and airframe, smooth engine running, and reduced noise levels. At present there is no efficient computational method of doing this for multi-spool engines within feasible time frames, and consequently, the nonlinear dynamics of such systems are poorly understood. Indeed, operational vibration measurements routinely reveal phenomena that cannot be predicted by current analytical studies of individual nonlinearly damped rotors considered in isolation. The proposed project concerns the creation of a tool for the efficient prediction of the nonlinear vibration of multi-spool aero-engine assemblies, and the analysis of such systems through its use. The objectives of the proposed project are: (i) to devise a computational tool that will significantly enhance the capabilities of the current rotordynamic modelling platforms; (ii) to investigate the vibration characteristics of an aero-engine assembly in the context of the theory of nonlinear dynamics; (iii) to construct a test rig that is a simplified model of a twin-shaft engine, for use as a laboratory demonstrator of nonlinear vibration phenomena; (iv) to establish guidelines for a rationalised approach towards designing SFDs into a typical aero-engine assembly. The research programme will integrate fundamental research into nonlinear dynamics theory with more applied research involving computational modelling and experimental validation. The results of this research would benefit primarily the aerospace industry, in its quest to develop lighter and more efficient engine designs while keeping up with ever more stringent safety requirements.