Coupled vibration of unshrouded centrifugal compressor impellers. Part II: Computation of vibration behavior

Abstract

The increased use of small gas turbines and turbochargers in different technical fields has led to the development of highly-loaded centrifugal compressors with extremely thin blades. Due to high rotational speed and the correspondingly high centrifugal loads, the shape of the impeller hub must also be optimized. This has led to a reduction of the thickness of the impeller disc in the outlet region. The thin parts of the impeller are very sensitive and may be damaged by the excitation of dangerous blade vibrations. Experimental investigations of coupled vibration behavior are presented in Part I of the paper. The results of these investigations were able to explain the dominance of coupling effects between the blades and the disc. Part II of the paper presented here describes finite element (FE) code computations of the vibration behavior of the blades and the complete impeller for two different impeller types - one with radial-ending blades and the other with backswept blades. The results are able to demonstrate the influence of coupling on dynamic behavior and the high importance of careful impeller design. The computational results were found to correspond very well with the results of the experimental investigations.