Ignacio LASALA, Eric BACH, Avidh S. BAVKAR, Guillermo PANIAGUA, Etienne CHOQUET, Thierry ANDRE

DOI Number: N/A

Conference number: HiSST-2025-278

Accurate total temperature measurements in high-speed flows are challenging due to unsteady probe–shock interactions, sensor-specific response characteristics, and errors arising from conduction, convection, radiation, and non-isentropic flow deceleration around the sensing element. While these error sources have been recognized and studied in the literature, most correction strategies treat them as independent, an assumption that breaks down in high-speed, high-temperature environments. Moreover, different total temperature probe designs exhibit varying sensitivities to these errors due to their distinct thermal and dynamic characteristics. This work assesses the accuracy of Fiber Bragg
Grating (FBG) sensors relative to a conventional thermocouple probe in high-speed flow. It evaluates, compares, and proposes correction methods for velocity and conduction errors in both probe types. This study evaluates temperature errors in an FBG temperature sensor housed in a Kiel shroud in sub- and supersonic jets at ambient and elevated temperatures. This is carried out side by side to a conventional thermocouple sensor enabling the comparison of both measurement technologies. The tests were conducted in the Facility for Instrumentation and Open jet Research (FIOR) of PETAL, which is a converging nozzle of 80 mm exhaust diameter, and seek to compare the velocity error and
conduction error of both types of probes, as well as to develop and evaluate a common correction methodology. Each dynamic test consisted of a temperature stabilization period of 15 minutes at Mach 0.45, and several stable blowdowns at Mach numbers ranging from 0.3 to 1.1 at both room temperature and heated conditions (100°C). The tests were coupled with IR videos that recorded the temperature at the probe support. The data from all tests were used to fit the temperature response to a combined velocity–conduction error model. This approach helps quantify the contribution of each error source to the sensor’s response and enables the retrieval of the true total temperature. The model requires as inputs the Mach number, the sensor reading, and the probe support temperature obtained from infrared measurements. Overall, this study provides a strong foundation for improving temperature measurement accuracy in high-speed flows and offers valuable insight into the performance of both FBG sensors and thermocouples for aerospace applications.

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