Experimental Investigation of Mistuning Effects on High Pressure Compressor Stators

Abstract

High pressure compressor (HPC) stator vanes of small gas turbine engines frequently have high circumferential variation of vibratory stress. This is very important for vibratory stress measurement by strain gauge tests and structural high cyclic fatigue characterization. The current paper presents experimental results of studying the effects of HPC stator angular positions in gas turbine engines on the circumferential distribution pattern of vibratory stress. Strain gauge tests were done on a stator with cantilevered vanes. Each vane had a strain gauge deployed at the same location. The stator was installed in gas turbine engines at two different angular positions during strain gauge tests. The experimental results show that more than one resonant peak occurred for a given vibratory mode and engine order resonance. The frequencies of resonant peaks were close to one another. The circumferential distribution of maximum vibratory stress (i.e., the maximum magnitude of these resonant peaks) with respect to the stator itself has a similar pattern at the two different angular positions. This clearly indicates the distribution pattern does not follow the gas-path aerodynamic pressure, but follows the stator angular positions. The frequency of the maximum vibratory stress was found to vary from sector to sector instead of from vane to vane; the vanes in each sector have a same frequency. Mistuning analysis was performed on the HPC stator to illustrate a number of resonant peaks and the sector-to-sector frequency variation of the maximum vibratory stress. The approach of “subset of nominal system modes” (SNM) [1, 2] was employed for mistuning analysis and the frequency distributions of stator vanes obtained by bench frequency response tests were used as input data. At the end, one might conclude that the high circumferential variation of vibratory stress be related to mistuning effects due to small variations in vane properties.