Experimental study of the dynamic behavior of gas foil bearings and its constructive controllability

气体轴承可作为小型和轻型涡轮机械的替代转子轴承类型，如涡轮增压器或小型燃气轮机。特别是在非常高的速度和很高的加工温度下，这种特殊形式的流体膜轴承使用气体而不是油作为润滑剂。省略了传统的润滑系统，降低了重量、维护和成本，并避免了润滑剂对工艺介质的污染。气体箔轴承(GFB)代表一种特殊类型的气体轴承。GFBs最大限度地减少了传统气体轴承使用弹性结构的一些主要缺点。这种弹性结构产生了额外的摩擦和阻尼，从而改善了稳定性。优化其动力特性的主要任务之一是尽量减少运行过程中产生的大次简谐振动。亚谐涡动频率与系统固有频率的重合可能会导致亚谐振幅的突然增加，这往往会导致损坏。目前已经有了减少GFBs减振的设计措施，从而增加了阻尼力和刚度。这些措施包括所谓的垫片等。各种初步研究表明，亚谐振动的开始及其幅度受垫片的影响。此外，研究还表明，可以在数值模拟的基础上对旋转振动的开始进行保守的预测，这对于使用GFBs的转子设计是非常重要的。然而，数值模拟的实验验证是缺失的。在拟议的项目中，计划对不同类型的GFB所需的线性化轴承参数进行系统的实验确定，以评估旋转频率。这导致了用于参数确定的数值模型的验证。该模型可用于进一步的转子动力学、稳定性和优化研究。在该项目中，建立了一个旋转动力学试验台，可以系统地研究GFBs中转子的非线性振动行为。这些实验将提供有关亚谐振动起始速度的信息，并对结构措施(如垫片)的有效性提供提示。总体结果将为各类燃气轮机的设计和研究提供高质量的数据，并为今后的整机模型(结构-外壳-轴承-转子)的验证和验证提供参考。

Gas-bearings can be used as an alternative rotor bearing type for small and light turbomachinery such as turbochargers or small gas turbines. Particularly at very high speeds and high process temperatures, this special form of fluid film bearings that uses gas instead of oil as a lubricant. The omission of a conventional lubrication system reduces weight, maintenance and cost and avoids contamination of process media from lubricants.The Gas Foil bearing (GFB) stands for a special type of gas bearings. GFBs minimize some of the major drawbacks of conventional gas bearing using an elastic structure within. That elastic structure creates additional friction and damping and thus improves stability properties. At the same time the load capacity can be increased.One of the main tasks in the optimization of dynamic properties of GFBs is to minimize the occurring large, subharmonic vibrations during operation. A coincidence of the subharmonic whirl frequencies with a system natural frequency can cause a sudden increase in the sub-harmonic amplitudes, which often leads to damage. Design measures for a vibration reduction of GFBs, leading to an increase in the damping and stiffness, already exist. These measures include, among others, so-called shims. Various preliminary studies have shown that the onset of subharmonic vibrations and their amplitudes are affected by shims. Furthermore, it was shown that conservative predictions of the onset of whirl vibration, which is very important for a design of rotors using GFBs, can be made on the basis of numerical simulations.However, an experimental validation of numerical simulations is missing. Within the proposed project a systematic experimental determination of the required linearized bearing parameters of different GFB types in order to assess the whirl frequency is planned. This results in a validation of a numerical model for parameter determination. That valid model will be used for further investigations on rotordynamics, stability and optimization. During the project a rotordynamic test bed is built that allows a systematical investigation of particularly nonlinear vibration behavior of a rotor in GFBs. The experiments will provide information about the onset speed of the subharmonic vibration as well as give hints on the effectiveness of structural measures such as shims. The overall results will provide a high quality of data for the design and research of various types of GFBs and serve future simulations of whole engine models (structure-housing-bearing-rotor) for verification and validation.