The Air Force requires a new measurement capability to monitor the surface temperature of thermally-barrier-coated blades and vanes on the first turbine stage of military fighter engines. Accurate quantification of temperature will allow increased performance of military fighter aircraft.
A method for measuring the surface temperature of blades and vanes in the hot section of turbine engines using a thermographic phosphor technique is being developed by NASA Glenn Research Center, Cleveland, Ohio in collaboration with AEDC and the Propulsion Instrumentation Working Group.
The measurement technique requires coating the blade and vane surfaces with a phosphor material appropriate for the targeted temperature range. The phosphor material is excited by a pulsed laser beam and the temperature determined from the time-rate-of-decay of the luminescence signal.
During a week of testing, NASA demonstrated the TGP measurement technique on a phosphor-coated engine vane section mounted in the exhaust flow field of an AEDC J85 engine at the University of Tennessee Space Institute Propulsion Research Facility. The J85 afterburner exhaust was used to simulate the temperatures experienced by the first stage turbine.
The test program was conducted in two phases; the first phase demonstrated an imaging TGP technique in which the laser and detection camera were mounted off to the side of the exhaust flow. The laser beam was directed to the test article mounted on a water-cooled stand. The camera viewed the surface of the coated vane and recorded two images of luminescence decay at different times after each laser pulse.
The second phase demonstrated an optical-probe that was inserted into the water-cooled mount to within an inch of the vane surface. This approach simulated insertion of the probe into the turbine section of an engine. The laser beam was transmitted through an optical fiber into the probe and focused onto a single spot on the vane surface. Optical fibers mounted around the laser fiber collected and transmitted the thermographic luminescence radiation to a photomultiplier detector located in the control room about 50 feet away from the engine. The fast response silicon detector recorded the temporal luminescence decay for each laser pulse. For both imaging and point measurement techniques, the temperature was deduced from the temporal decay; two images displaced in time for the imaging technique, and the continuous decay signal recorded for the single point probe technique. An eight micron-wavelength pyrometer system was used to independently monitor the temperature of the vane surface during both phases of testing.
Jeff Eldridge, the NASA Glenn Research Center project manager for the test, expressed appreciation for the excellent support provided by the ATA Technology staff and praised the J85 PRF as a great environment for research, particularly for transitioning laboratory technology to engine test maturity.
NASA successfully demonstrated the TGP temperature imaging technique under pseudo realistic engine conditions as well as a fast response, engine-insertable temperature probe that may be suitable for direct measurement of rotating blades’ temperatures.
Eldridge stated, “The combination of a unique test facility with excellent support makes testing at the Propulsion Research Facility a great value. Based on our experience, I hope we have an opportunity to test again in the future.”