Development of a Novel Optical Instrument for Turbine Blade Vibration Analysis

摘要

We discuss the development of a compact novel instrument based on phase-shifting interferometry for thestudy of turbine blade vibrational modes. Unlike conventional phase-shifting interferometers, whichgenerally require multiple exposures or multiple cameras, this instrument achieves the accuracy andresolution of phase-shifting in a single shot with a single camera. Data acquisition, reduction andpresentation are effectively in real time. The light source is a CW solid-state green laser radiating at 532nm that is coupled to an acousto-optic modulator for time gating. This permits investigation of the blademode structure during specific phases of a vibration cycle. Spatial resolution over the surface of the bladeis approximately 1 mm, while the resolution in the line of sight is better than λ/20, or 25 nm. The field ofview is about 150 mm × 150 mm at a target distance of 1 meter. Results obtained in the laboratory, usinga piezo-electrically driven shaker, will be presented and discussed.The instrument in its present form is designed for the study of static or slowly rotating blades. Theultimate goal is to monitor blade vibrational states in a working turbine under operational conditions.This will require several modifications to the present design, including the use of fiber optic coupling andmore sophisticated lasers. The feasibility and limitations of these advances will be discussed.