High cycle fatigue is a continuous research topic within the turbomachine community. One field of the investigations is the fluid-structure interaction of 2-D impellers, which can be simplified as disks with their surrounding side cavities. In modern machines the pressure ratios tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the disk structure play an important role in machine design. However, they are not fully understood, yet. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at higher pressure levels. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood.
This paper summarizes the test rig setup and focuses on one of the main findings of an extensive experimental research project, which investigated the fluid-structure interaction of a disk with side cavities, at the University of Duisburg-Essen. The focus lays on the damping behavior of strongly coupled acoustic and structure modes.
Measurement results gathered at the aeroacoustic test rig are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the half-width method. Compared to the weakly coupled structure mode, the damping of the strongly coupled structure mode is some orders higher at atmospheric pressure conditions. The damping ratio decreases with an increasing pressure level, however still remains some orders higher, than the damping of weakly coupled structure modes.