| dc.description.abstract | Experience, theoretical and practical, investigations are presented on two radial flow high-speed turbines, which showed unacceptable high subsynchronous vibrations during operation onsite. The first example deals with a two-stage integrally geared turbine for energy recovery, with generator brake installed in a chemical plant. Measurements and calculations ruled out that the subsynchronous vibrations were caused by the bearings. Measurements of pressure at the inlet and outlet of both stages and in the inter-stage pipe hinted at an acoustic excitation in the annular space between impeller and adjustable nozzle ring. The acoustic excitation and resulting subsynchronous vibrations could be reduced by installing a few fixed nozzles, thus interrupting the vaneless space to the extent that safe operation of the gear turbine is possible adhering to the relevant guidelines. The second example is a compressor-loaded turbine with bilaterally overhung radial impellers employed in an air separation plant. Non-reproducible, subsynchronous vibrations occurred, due to variations of manufacturing tolerances of bearing geometry, labyrinth seals and gap geometries representing the main causes. The results of parameter studies in the bearing and sealing zones showed that the damping effect of the bearings can be eliminated by the influence of the labyrinths. Thus, the rotor becomes unstable. The rotor was stabilized by the installation of swirl brakes and antiswirl sleeves. After that, subsynchronous vibrations ceased to exist resulting in stable and safe operation. | en |
