Fiber Bragg Grating Total Temperature Probes for High-Speed Airflow With High Recovery Factor

The fiber Bragg grating (FBG) temperature measurement technology has advantages, such as high accuracy, small size, anti-interference, and stable performance compared to traditional thermocouple technology in high-speed airflow total temperature testing. However, low recovery factors of FBG total temperature probes at low Mach numbers have been reported, which is very detrimental to improving the accuracy of the total temperature measurement. In this article, a 3-D structure model of FBG total temperature probe is established based on the characteristics of fiber as the temperature sensing element. The temperature distribution under different probe structural parameters, such as the inner diameter of the shield, the position, and length of FBG, is analyzed using conjugate heat transfer (CHT) multiphysics field model. Combined with coupled-mode theory, the spectral characteristics of different FBG parameters and their effects on the recovery factor are analyzed. The structure of FBG total temperature probe with high recovery factor is designed. The comparative experimental results of high-speed airflow show that the improved FBG total temperature probe has a recovery factor exceeding 0.92 from Mach number 0.3–0.8 and up to 0.99 at Mach number greater than 0.4, which has even exceeded the level of most traditional thermocouple total temperature probes.