Time-resolved stagnation temperature measurements in hypersonic flows using surface junction thermocouples

Abstract

Fast-response coaxial surface junction thermocouples have been used to measure time-resolved stagnation temperature of the Mach 6 flow produced by the University of Southern Queensland’s hypersonic wind tunnel, TUSQ. The piston compression and the nozzle expansion of the test gas were found to be approximately isentropic for the first 65 ms of flow. Thereafter, the stagnation temperature reduces from T0≈560K due to the heat lost to the cold barrel, and this process can be modelled based on the measured barrel pressure history to simulate the stagnation temperature in TUSQ to within 2% of the actual value for the first 150 ms of flow. By operating the thermocouples at the flow stagnation temperature, the fluctuations of the flow stagnation temperature were investigated. A 3–4 kHz narrowband stagnation temperature fluctuation appearing after t≈65ms was measured, and found to be correlated with the transition to turbulence of the flow in the barrel.