PULSED HOLOGRAPHIC VIBRATION ANALYSIS ON HIGH-SPEED ROTATING OBJECTS - FRINGE FORMATION, RECORDING TECHNIQUES, AND PRACTICAL APPLICATIONS

The pulsed laser holographic vibration analysis on high-speed rotating structures presents several difficulties due to the rotational movement of the object between the two laser pulses recording the holographic interferogram. Apart from the vibrational motion, the recorded holographic fringes can be additionally modulated due to the object's rotary motion. Beyond small angles of rotation, a decorrelation of the recorded object waves occurs, preventing the formation of high-visibility interference fringes. To overcome these effects, different holographic recording techniques were used, including an interferometer in which both the reference wave and the holographic recording plate are rotated simultaneously in relation to the object and an interferometer incorporating an image derotator. Conditions for the practical application of these experiments are outlined, and examples of vibrational studies of high-speed rotating components, i.e., cantilever beams, disks, cooling fans, and radial impellers, are presented. The radial impeller vibration investigation was done on a compressor test facility up to object speeds of more than 13,000 rpm, corresponding to a circumferential speed of approximately 200 m/s.