Compressor Blade Vibration Measurements Using Blade Image Velocimetry

This paper discusses the application of a novel vibration measurement technique, termed blade image velocimetry (BIV), to a high-speed axial compressor. Measurements of compressor blade vibration can be difficult to obtain and are critical to aeromechanical design validation. The measurement technique discussed in this paper used a commercial particle image velocimetry (PIV) system and was developed as an alternative to conventional measurement techniques such as strain gages and blade tip timing (BTT). The measurement principles and error analysis are reviewed. Methods for estimating the magnitude of random noise corrupting the measurement and validating the vibration amplitude estimates are presented. The technique was validated using a 1.5 stage axial compressor operating at low shaft speed, where it measured the tip velocity to within 0.02% of the true value. The technique was then used to investigate blade vibration at high shaft speed. Low amplitude vibrations in first bending and first torsion were discovered when the compressor was operated at design air-mass flow rate. These vibrations had a maximum tip deflection of 15 mu m for bending and 7 mu m for torsion. The vibration amplitude for first bending and first torsion tripled when the compressor was operated at low air mass-flow rate, corresponding to deep stall. Furthermore, excitation of the third eigenmode was also measured. The maximum tip deflections of the first three eigenmodes when the compressor was operated at deep stall were 47 mu m, 27 mu m, and 15 mu m, respectively.