ANALYSING NON-SYNCHRONOUS BLADE VIBRATIONS IN A TRANSONIC COMPRESSOR ROTOR

This paper aims to add to the understanding of non-synchronous blade vibration caused by unsteady flow close to the stability limit of transonic compressor rotors. Blade vibrations are measured in the rotating frame of reference by strain gauges applied to the blades and additionally in the stationary frame of reference by capacitive tip clearance/tip timing sensors. Furthermore unsteady pressure transducers in the casing wall are used to analyse the flow phenomena during high blade vibration amplitudes. During the transient experiments, the compressor is back-pressured into its stability limit. Two transient measurements of a compressor setup with an enlarged tip clearance of 2.5% blade chord are analysed at part speed and design speed. This means that subsonic and transonic operation conditions are analysed. In both cases, nonsynchronous vibration occurred and limited the compressor operation. The mechanism leading to these vibrations is based on an unsteady flow pattern that rotates relative to the rotor, reported as rotating instability.