Nonlinear vibration of multi-spool aero-engine assemblies

大多数现代喷气发动机都是由两个或三个同轴嵌套转子组成的多轴总成，以不同的、模糊相关的速度旋转。由于与轴承一起使用的油膜阻尼器（挤压膜阻尼器- SFDs）引入了所谓的非线性，这种系统的振动特性相当复杂。将这种非线性元件设计到总成中是一个棘手的问题，因为它可能会对发动机的加速和减速产生振幅跳变，以及与转速不同步的振动。预测和分析这种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来在可行的时间框架内完成多轴发动机的非线性动力学，因此，人们对这类系统的非线性动力学知之甚少。事实上，运行振动测量通常会揭示当前孤立考虑的单个非线性阻尼转子的分析研究无法预测的现象。提出的项目涉及创建一种工具，用于有效预测多轴航空发动机组件的非线性振动，并通过其使用对此类系统进行分析。建议项目的目标是：(i)设计一种计算工具，以显著提高当前旋转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总成的振动特性；（iii）建造一个简化双轴发动机模型的试验台，用作非线性振动现象的实验室演示；（iv）制定指引，以合理的方法将SFDs设计成典型的航空发动机组件。该研究计划将把非线性动力学理论的基础研究与更多涉及计算建模和实验验证的应用研究结合起来。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，更高效的发动机设计，同时保持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.