Blade Vibration on Centrifugal Compressors - Fundamental Considerations and Initial Measurements

Abstract

Blade vibration has to be considered in the design of high pressure ratio / high mass flow centrifugal compressors with increasing rotational speed values due to the reduced blade thickness. Results of a theoretical and experimental investigation concerning this problem are described. FE calculations of the stress distribution on the blade for the lower natural frequencies and various vibration tests at rest were carried out to investigate resonance and damping effects. This preparatory work was aimed at determining blade vibration behavior and acquiring fundamental experience for measurements on compressors in operation. Results of blade vibration measurements on compressors with a vaneless diffuser carried out with semiconductor strain gages and an 8-channel telemetry system are presented for constant rotational speed and for constant throttle valve position, and indicate considerable blade excitation during stall effects. Simultaneous flow measurements complete the investigation to determine the causes of blade vibration. For example, investigations were made of the extent of blade resonance excitation due to non-uniformity of the flow downstream of the impeller or due to flow disturbances caused by carrier blades for bearings in the compressor inlet and simulated by spoilers. © Freund Publishing House Ltd.