Dynamic Total Temperature Measurement in High-Speed Airflow Using Short FBGs

Dynamic testing of the total temperature of subsonic airflow is essential for comprehending the inlet flow distortion of aircraft gas turbines. This article introduces a technique for the measurement of dynamic total temperature in subsonic airflow using a short fiber Bragg grating (FBG). A thermal response model of FBG in subsonic flow was established based on Newton’s law of cooling. By means of the coupled mode theory and Monte Carlo analysis, the relationship between grating length and spectral signal-to-noise ratio (SNR) with demodulation standard deviation was revealed. A total temperature sensor with short 0.5-mm FBGs was fabricated and characterized experimentally in airflow up to Mach 0.7. At Mach numbers greater than 0.5, the temperature measurement error of the sensor is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~^{\circ }$ </tex-math></inline-formula>C at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$300~^{\circ }$ </tex-math></inline-formula>C. The response time has been demonstrated to be less than 40 ms in the Mach range of 0.2–0.7. This indicates that the FBG-based total temperature sensor has great potential for applications in high-speed airflow measurement, not only in steady-state airflow testing but also in dynamic airflow total temperature measurement.