High-speed blade vibration in a transonic compressor

Abstract

This experiment was conducted to measure transverse vibrations of the blades in a transonic compressor rig at the Naval Postgraduate School. The compressor was instrumented with non-invasive laser light probes to measure changes in time of arrival of all the blades, relative to an expected arrival time. These times were then converted to blade deflections. Results proved that the primary observed vibration was a first bending mode. The frequencies that excited this mode precisely correlated with NASA predictions. It was shown that the modal frequency for the first bending mode was dependent on engine speed as a result of the untwisting blade. Maximum observed blade deflection was proved to occur during the surge event, resulting in maximum blade fatigue. It was concluded that certain operating regimes, with large blade deflections, should be avoided to extend blade life by limiting fatigue.