INTERFEROMETRIC FIBER SENSORS FOR MEASUREMENT OF SURFACE HEAT-TRANSFER RATES ON TURBINE-BLADES

We describe a prototype sensor for surface heat transfer measurements based on a miniature fibre Fabry-Perot (FFP) interferometer. These sensors are being developed for a particular application where heat transfer data are currently obtained using conventional platinum thin film resistance thermometers. The specification that the sensors must exceed is: (i) temperature resolution of 25 mK over a 50 K range; (ii) temporal response of 10-mu-s; (iii) an ability to operate as a calorimetric heat transfer gauge. The sensor consists of a short length of single mode optical fibre (approximately 3 mm) to which low reflectivity coatings have been applied at each end. It is illuminated and interrogated by an arbitrary length of addressing fibre. A laser diode is used as the source and we have exploited the facility to frequency modulate the diode in a novel signal processing scheme. To determine the performance of the sensor, short duration heat pulses derived from a pulsed Nd:YAG laser were applied to one end of the FFP. The response time was found to be 8-mu-s and the sensor operation as a calorimeter was verified.