Influence of axial bearing dynamics on rotor vibrations: Transient analysis considering cavitation and coupling of axial and radial fluid films

除了转子的弹性和惯性特性以及外部载荷外，转子系统的振动特性主要由轴承决定。由于其优越的机械和热特性以及低成本，流体动力轴承结构经常被使用。一方面，这适用于轴向轴承，它主要影响弯曲振动，同时推力轴承用于考虑轴向载荷。由于它们各自的刚度和阻尼参数，这两种轴承类型对系统的行为都有很大的影响，这对产生的振动和稳定性有很大的影响。不断的进步和不断增加的需求需要提高瞬态系统行为的仿真质量，这就是为什么转子系统，轴承及其相互作用的系统特性的详细建模是必要的。对于瞬态研究，在耦合转子轴承仿真领域使用已建立的稳态解是不可能的。虽然非线性方程系统的解对于轴承状况的准平稳考虑是足够的，但对于转子动力学方面的瞬态问题必须进行时间积分。考虑到时变空化状态，对轴承的相应详细考虑使得在时间积分的每一步都需要对雷诺微分方程进行评估。在之前的项目中，基于Elrod的方法，针对轴颈和浮环轴承开发了一种改进的空化算法，现在将其转移到推力轴承上。在这种情况下，除了简单的止推轴承外，还会出现各种其他形式的结构，可分为组合轴承（组合轴颈和止推轴承），浮动圆盘轴承和倾斜垫轴承。轴向润滑膜和径向润滑膜之间的液力联轴器以及转子轴承系统各部件在气蚀作用下的机械联轴器必须加以考虑。扩展的仿真模型旨在有效地预测频率和振幅相关的振动现象（次谐波振动、外载荷后向旋转激励、倾斜垫颤振）。

In addition to the elastic and inertia properties of the rotor as well as the external loads, the vibration behaviour of rotor systems is mainly determined by the bearings. Due to the advantageous mechanical and thermal characteristics as well as the low cost, hydrodynamic bearing constructions are often used. On the one hand, this applies to the journal bearings, which dominantly influence the bending vibrations, and at the same time thrust bearings are used to account for axial loads. Due to their respective stiffness and damping parameters, both bearing types significantly contribute to the system behaviour, which has a drastic effect on the resulting vibrations and stability. Continuous advancements and increasing demands require an improved simulation quality of transient system behaviour, which is why detailed modelling of the system properties of the rotor system, bearings and their interactions are necessary.For transient studies, it is not adequately possible to use established steady-state solutions in the field of coupled rotor bearing simulation. While the solution of a non-linear equation system is sufficient for quasi-stationary considerations of the bearing situation, time integrations must be carried out for transient questions with respect to rotor dynamics. A correspondingly detailed consideration of the bearing makes the evaluation of the Reynolds differential equation necessary at each step of the time integration, taking into account the time-variant cavitation state. In the previous project, a modified cavitation algorithm was developed for journal and floating ring bearings based on Elrod’s approach, which is now to be transferred to thrust bearings. In this context, in addition to the simple thrust bearing, various other forms of construction occur, which can be divided into combi bearings (combined journal and thrust bearings), floating disc bearings and tilting pad bearings. Hydraulic couplings between axial and radial lubricating films as well as mechanical couplings to the components of the rotor bearing system under the influence of cavitation must be taken into account. The extended simulation model is intended to validly predict relevant vibration phenomena (subharmonic vibrations, backward whirl excitation by external loads, tilting pad flutter) concerning both frequency and amplitude.