NONLINEAR DYNAMIC ANALYSIS OF OIL-FREE TURBOMACHINERY

无油涡轮机械是一种新兴的技术，被定义为高速旋转机械，没有油润滑转子支撑。该术语通常被理解为指气体轴承技术，特别是箔-空气轴承。这种轴承通过由柔性箔结构包围的气垫来支撑轴。箔结构的引入解决了与平面空气轴承所需的非常紧密的径向间隙相关的问题。与箔空气轴承，而轴是静止的，有一个轻微的间隙或轴和轴承之间的预紧力。当轴转动时，产生压力，将箔边界推开，使轴完全在空中飞行。在轴和/或顶部箔上的固体润滑剂涂层允许在启动和关闭期间短暂的摩擦间隔。美国固体润滑剂技术的最新技术突破将使这种轴承广泛应用于涡轮机械，特别是燃气轮机机械。这导致了对无油涡轮机械的深入研究，其技术和环境效益为军事和民用应用（例如涡轮增压器高达180,000rpm和小型飞机发动机）提供了动力。正如美国宇航局所说，这项技术的首要挑战是设计一种无油涡轮发动机，为21世纪的飞机提供动力。箔空气轴承，像传统的油轴承一样，是非线性元件，能够在系统的动态响应中引入不良的非线性效应。这些影响可能包括振动幅度的突然跳跃、非同步振动和自激振动。这些影响加剧了振动并引起疲劳。因此，为了保证结构的完整性，这些轴承在实际机械中的部署需要考虑轴承非线性的转子动力学分析。对这种影响作出可靠的定量预测的能力使工程师能够在设计中考虑/减轻它们。此外，这种分析为在职监测提供了急需的知识库基础。然而，这种计算受到轴承模型复杂性带来的高昂计算成本的阻碍。因此，到目前为止，动力学分析仅限于高度简化的转子动力学系统。本课题旨在研究实用无油涡轮机械非线性动态分析的新方法。这些方法将在一项研究中得到实验验证，该研究将为此类系统的非线性动力学提供急需的见解。该项目的可交付成果将是：1。一套基于三种新方法（伽辽金约简、谐波平衡、系统识别）的有效非线性动态分析的计算机软件算法。2。一个原始设计的试验台，用于对计算方法进行实验验证。一份关于方法验证的报告，着重于计算和实验问题。拟议中的研究是新颖的，因为：(a)它将使英国在无油涡轮机械技术方面站稳脚跟，提高英国的科学形象——迄今为止，此类研究主要局限于美国；(b)研究实际无油涡轮机械（如无油涡轮增压器）的非线性动力学预测；(c)它将通过上述三种新办法做到这一点；(d)它将制作一个原始设计的试验台，以验证所开发的方法和对非线性现象的研究。这项工作将由一名博士后研究员进行，为期三年。

Oil-free turbomachinery is an emerging technology defined as high speed rotating machinery that operates without oil-lubricated rotor supports. The term is generally understood to refer to gas-bearing technology, in particular, foil-air bearings. Such bearings support the shaft by means of an air cushion bounded by a flexible foil structure. The introduction of the foil structure resolves the problems associated with the very tight radial clearance required by a plain air bearing. With a foil-air bearing, while the shaft is stationary, there is either a slight clearance or a preload between shaft and bearing. As the shaft turns, a pressure is generated, which pushes the foil boundary away, allowing the shaft to become completely airborne. A solid lubricant coating on the shaft and/or top foil allows for the brief rubbing interval during start-up and shutdown. Recent technological breakthroughs in the USA in solid lubricant technology will enable the widespread use of such bearings in turbomachinery, particularly gas turbine machinery. This has resulted in intensive research in oil-free turbomachinery motivated by its technological and environmental benefits for both military and civil applications (e.g. turbochargers that run up to 180,000rpm and engines for small aircraft). As stated by NASA, the foremost challenge for this technology is the design of an oil-free turbine engine to power 21st century aircraft .Foil-air bearings, like conventional oil bearings, are nonlinear elements that are capable of introducing undesirable nonlinear effects into the dynamic response of the system. These effects may involve sudden jumps in the vibration amplitude, non-synchronous vibration and self-excited vibration. These effects exacerbate vibration and introduce fatigue. Hence, to guarantee structural integrity, the deployment of these bearings in practical machinery necessitates rotordynamic analysis that takes account of the bearing nonlinearity. The ability to make reliable quantitative predictions of such effects enables the engineer to account for/mitigate them in the design. Moreover, such analysis provides the basis of a much-needed knowledge database for in-service monitoring. However, such calculations are hampered by the prohibitive computational cost introduced by the complexity of the bearing model. Consequently, dynamic analysis has so far been restricted to a highly simplified rotordynamic system. The proposed project researches novel methods that enable the efficient nonlinear dynamic analysis of practical oil-free turbomachinery. These methods will be experimentally validated in a study that provides a much-needed insight into the nonlinear dynamics of such systems. The deliverables of this project will be:i. A suite of computer software algorithms for efficient nonlinear dynamic analysis based on three novel approaches (Galerkin reduction, Harmonic Balance, System Identification). ii. An original-design test-rig for experimental validation of the computational methods.iii. A report on the validation of the methods, focussing on both computational and experimental issues.The proposed research is novel since: (a) It will give the UK a foothold in oil-free turbomachinery technology, raising the UK's scientific profile - such research has to date been confined mainly to the US; (b) It will research the prediction of the nonlinear dynamics of practical oil-free turbomachinery (e.g. an oil-free turbocharger); (c) It will do so through the three novel approaches mentioned above; (d) It will produce an original-design test-rig for the validation of the methods developed and investigation of nonlinear phenomena.The work will be carried out by a post-doctoral researcher over a period of three years.