Blade Vibration on Centrifugal Compressors: Blade Response to Different Excitation Conditions

Abstract

Results and analysis of blade vibration measurements on a high pressure ratio / high mass flow centrifugal compressor made with strain gages and using multichannel telemetry are described for compressors with 3 different types of vaned diffusers. Considerable high frequency blade excitation and vibration of the shallow region near the impeller outlet were observed. Initial progress to predict this dangerous excitation caused by the diffuser vanes was made with the help of FE computations using a simplified element system consisting of the vibrating zones of a 90° sector of the impeller. Satisfactory agreement with measured vibration data was achieved. The influence of rotating stall on blade excitation was investigated using different types of vaned diffusers leading to different numbers of rotating stall zones and variations in the rotational speed of the cells. Blade vibration intensity due to surge in conjunction with variations of the diffuser is also considered. Holographic interferometry was successfully applied to blade vibration measurements on compressors in operation. The investigation was aimed at studying the occurrence of blade modes and the vibratory behavior of the different blades near the interesting inlet zone. The occurrence of different constellations of blade modes at a resonance point and at an operating point far from resonance was demonstrated.