LASER VIBROMETRY MEASUREMENTS OF ROTATING BLADE VIBRATIONS

One of the most important design factors in modern turbormachinery is the vibration of turbomachinery blading. There is a need for del elopi ng an in-service, noncontacting, noninterfering method for the measure ment and monitoring of gas turbine, jet engine, and steam turbine blad e vibrations and stresses. Such a technique would also be useful for m onitoring rotating helicopter blades. In the power generation industry blade failures can result in millions of dollars of downtime. The mea surement of blade vibrations and dynamic stresses is an important guid e for preventive maintenance, which can be a major contributor to the availability of steam turbine, gas turbine, and helicopter operations. An experiment is designed to verify the feasibility of such a vibrati on monitoring system using the reference beam on-axis laser-Doppler te chnique. The experimental setup consists of two flat, cantilever blade s mounted on a hub attached to the shaft of a dc motor. The motor rest s on a linear bearing permitting motion only in the direction of the m otor shaft. The motor and blade assembly is then excited via an electr odynamic shaker at the first natural frequency of the blades. The resu lting blade vibration is then detected using a laser vibrometer. The v ibration frequencies and amplitudes of the two rotating blades are suc cessfully measured.