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

涡轮机中的叶轮侧间隙通常由径向叶轮的轮毂和护罩盘的外壁以及壳体的内壁限定。转子定子腔充满流体，并且由于密封件处的泄漏，根据机器的操作条件，存在径向向内或径向向外的通流。除了侧腔中的复杂流动结构之外，还发生压力波动，其激发流体体积振动。流体和盘结构的现有耦合导致盘的振动，这能够在盘处引起相当大的损坏。特别是在流体的高压和相应的高密度的情况下，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空腔中声模态的发展有很大的影响，对叶轮盘的振动特性有很大的影响，本项目将在专门搭建的试验装置中再现流体和盘的声激励，并研究盘旋转、通流量、实验研究了通流方向和通流周向速度分量对声模形成的影响。现有的通用试验设备对于确定振动特性试验的边界条件是必不可少的。为了达到描述基本现象的目的，重要的是使用不受涡轮机毂盘或护罩盘的技术要求限制的盘几何形状。为了支持理想的基础研究，圆盘应该近似于一个平面，外壳应该是平的，没有任何边缘。以这种方式，产生“理论”转子定子腔。通过这种方式，所获得的基本结果不仅可以被用于声学，而且可以有助于对由声压波动激励的充满流体的腔中的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.