A new method of remote thermometry utilizing the temperature dependent optical
properties of thermographic phosphors was evaluated for use in measuring high-pressure
turbine blade metal temperatures in an operating turbofan engine test rig. Thermographic
phosphors, ceramics doped with a rare earth metal, were bonded to the turbine blades.
These phosphors exhibit fluorescence when optically excited by a laser, and both the
intensity and the rate of decay of the fluorescence are temperature dependent An optical
fiber probe was used to carry the excitation laser light to the blade surface, and to receive
the resulting fluorescence. The blades rotated at speeds up to 30,000 rpm.
Synchronization was achieved by a digital pattern recognition circuit, capable of locating
a specific blade with each revolution. The investigation concentrated on thennographic
phosphor characteristics, phosphor binding methods, and probe optical efficiency.
Although poor performance of the selected phosphor binding methods impeded the
location of the fluorescence signal in the operating gas turbine engine, many operating
characteristics of the technique were determined, and the new measurement technique was established as a promising candidate for further research in the temperature measurement of rotating surfaces inside a turbine engine.
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