High-Response Total Temperature Distortion Measurement

This proposal by MetroLaser Inc., describes in detail the design, calibration and deployment of a fiber-optic microsensor array designed to meet or exceed Air Force performance specifications for high-response inlet gas temperature measurements. Theproposal seeks to provide a comprehensive overview of the microsensor characteristics, fabrication methods, probe deployment for gas total-temperature measurements, and array networking for distributed engine inlet gas-temperature measurements. We describea fast-response fiber-optic microsensor measuring only 0.005 inch in diameter comprising a solid etalon or Fabry-Perot microcavity, formed by ion-assisted deposition of thin film multilayers on monomode optical fibers. Based on our analysis and relevantexperimental data obtained in shock tests and in a gas-turbine research facility, we anticipate the microsensor will provide a temperature resolution of 0.1 K, maximum working temperature up to 650 K, with a thermal bandwidth response in excess of 50 kHz.In addition, we describe a scheme for parallel multiplexing of fiber-optic microsensors using inexpensive commercial off-the-shelf telecommunications components such as fiber couplers, laser diodes and photodetectors which will enable inlet-distributed gastotal-temperature measurements at up to 48 positions simultaneously. The requirement to measure gas total-temperature at multiple upstream locations while simultaneously monitoring engine response, places strict limitations on flow blockage andconsequently on probe-deployed temperature sensor dimensions. The fiber-optic total-temperature microsensor array detailed in this report will provide distributed engine relevant data with unprecedented spatial and temporal resolution to elucidate the roleof inlet gas temperature distortion on engine performance. The data will provide for validation and refinement of computational fluid dynamics (CFD) models that predict the complex unsteady flow through engine stages, including inlets, compressors, andturbines. The proposed experimental technique and associated instrumentation therefore contributes towards efforts to improve aeroengine efficiency and to reduce development and operating costs. A broader range of applications is also anticipated to followfrom developments to further extend the maximum operating temperature to the limits imposed by silica quartz fiber (1100K). In its proposed implementation, the fiber-optic microsensor would be suited to various bio-medical applications that could includeorgan, tissue, arterial and intracranial temperature monitoring. The sensor is more broadly applicable to industrial process-control and monitoring in general, but in particular, where corrosive, combustive/explosive, high EMI or harsh radiationenvironments prevent the application of conventional temperature sensors. Similar design principles and considerations also apply to the implementation of a complementary high response total pressure sensor for aerodynamic applications and to othermeasurands with the longer term prospect of probe deployed sensor suites configured to measure specific parameters of interest.