Fast response co-axial thermocouple for short duration impulse facilities

A fast response Chromel-Alumel (K-type) co-axial thermocouple is designed, fabricated, calibrated and tested in a shock tunnel. The freestream Mach number of 5.75 and the total enthalpy of 0.92 MJ/kg are simulated to study the stagnation point heat flux of a hemi-spherical model through transient temperature trace. The realized K-type co-axial thermocouple of 3 mm in length and 1.6 mm in diameter is flush mounted at the stagnation point of a 7.5 mm radius hemi-spherical model. The achieved response time of the realized K-type co-axial thermocouple is ~3 µs, which is sufficient enough to capture the transient temperature signal. A steady tunnel flow time of 1.8 milliseconds is used to get the average stagnation point heat flux. The measured stagnation point heat flux is 22.96 W/cm2, which is well matched with the Fay-Riddell value within 5.5%. The realized K-type co-axial thermocouple is robust, responds fast, and can be contoured to any type of model surface.