The Cumulative Effects of Forcing Function, Damping, and Mistuning on Blade Forced Response in a High Speed Centrifugal Compressor With Inlet Distortion

Abstract

The vibratory response amplitude of a blade under forced response conditions depends primarily on the aerodynamic excitation amplitude, on damping, and on the effects of mistuning. The work presented here targets to identify the individual contribution of these parameters to the resultant response amplitude depending on the mass flow and the resonance case. For this purpose, measurements were performed of the excitation amplitude, damping, and response amplitude for a high-speed centrifugal compressor. The inlet flow field was intentionally distorted in order to target specific excitation cases of the first main blade mode. For the compressor used, it was found that the overall damping of the first mode could be considered to be constant for any resonance case and mass flow. For this reason, case-to-case variations in the blade-averaged response amplitude were found to depend solely on the aerodynamic excitation amplitude due to inlet flow distortion. Based on an examination of the aerodynamic work distribution during resonance, zones of either excitation or damping work on the blade surface could be successfully identified. This enabled the conclusion to be drawn that energy transfer is a very localized phenomenon and may significantly change as the mass flow is altered, thereby introducing a redistribution of the blade excitation function. The effect of mistuning was shown to alter aerodynamic damping and response amplitude. However, the variation in aerodynamic damping of individual blades was relatively low, thus suggesting that blade-to-blade variation in response amplitude is primarily driven by energy localization in the sense typically experienced with coupled and mistuned structures.