Fundamental investigation on the impact of a swirling through-flow in a rotating cavity on the formation of acoustic modes

叶轮机叶轮侧间隙通常受径向叶轮轮毂外壁、叶冠盘外壁和机匣内壁的限制。转子定子腔内充满流体，由于密封处有泄漏，根据机器的运行条件，有径向向内或径向向外的通流。除了侧腔内复杂的流动结构外，还会发生压力波动，从而激发流体体积产生振动。现有的流体和磁盘结构的耦合导致磁盘的振动，这能够在磁盘上引起相当大的损坏。特别是在高压和相应的高密度流体的情况下，激发的振动可能是有害的。此外，现有的流动结构和流体参数对腔内声模态的发展有很强的影响，对叶轮盘的振动特性也有显著影响。本项目将在专门搭建的测试设备上再现流体和圆盘的声激励，并通过实验研究圆盘旋转、通流量、通流方向和通流的周向速度分量对声模态形成的影响。现有的通用试验设备对于确定影响振动特性的试验的边界条件是必不可少的。为了达到研究基本现象的目的，重要的是使用不受涡轮机轮毂或叶冠盘技术要求的圆盘几何形状。为了支持所期望的基础研究，磁盘应该近似为一个平面，并且外壳也应该实现平坦且没有任何边缘。通过这种方式，产生了一个“学术”转子定子腔。这样，所获得的基本发现不仅可以用于涡轮机器，而且可以有助于对由声压波动激发的充满流体的腔中圆盘的振动行为的一般理解。

Impeller side clearances in turbomachines usually are confined by the outer walls of the hub and the shroud disk of the radial impeller and the inner walls of the casing. The rotor stator cavities are filled with fluid and because of a leakage at the seals there is a through-flow radial inward or radial outward depending on the operating conditions of the machine. Beside the complex flow structure in the side cavities pressure fluctuations occur which excite the fluid volume to vibrations. The existing coupling of the fluid and the disk structure leads to vibrations of the disk which are able to provoke considerable damage at the disks. Particularly in case of high pressure and a corresponding high density of the fluid the excited vibrations can be harmful. In addition, the existing flow structure and the fluid parameters have a strong impact on the development of acoustic modes in the cavities and influence the vibration characteristic of the impeller disks significantly.The acoustic excitation of the fluid and the disk will be reproduced in this project in a specially raised test facility and the impact of disk rotation, amount of through-flow, through-flow direction and cir-cumferential velocity component of through-flow on the formation of acoustic modes will be investi-gated experimentally. The available generic test facility is essential for specification of the boundary conditions for the tests which shape the vibration behavior. In order to reach the target of investigat-ing basic phenomena it is important to use a disk geometry which is not subject to the technical re-quirements of a hub or a shroud disk of a turbomachine. Supporting the aspired basic research the disk should be approximated by a flat surface and the casing should be realized flat and without any rims as well. In this way an “academic” rotor stator cavity is generated. In this way the gained basic findings can be adopted not only for turbomachines but can contribute to a general understanding of the vibration behavior of a disk in a fluid filled cavity excited by acoustic pressure fluctuations.