Total temperature measurement of fast air streams with fibre-optic Bragg grating sensors

The suitability of using fibre Bragg gratings (FBG) as sensor elements in total temperature probes for turbine compressor applications is shown. A series of five FBG-based probes were built and characterized experimentally in the harsh environment of an open-jet test bench at air stream velocities of up to Mach 0.8. The performances of the FBG-based probes were compared with that of a conventional thermocouple-based total temperature sensor. All fibre-optic probes showed good mechanical robustness and recovery factors in the range of 0.79 to 0.99. Employing fibre-optic sensor elements allowed a significant reduction of the diameters of the stagnation tubes of the transducers. Because of the smaller probe design and thinner signal transmission cables, less distortion of the air stream is expected with the fibre-optic sensors, when compared to conventional instrumentation.