Analysis of Fast Thin-Film Temperature Gauges for Hypersonic Environments

Thin-film temperature gauges with nickel and silver sensing elements on a Macor ceramic substrate are evaluated for unsteady heat flux measurements in impulse facilities such as shock tunnels. Unsteady heat transfer simulations with known input heat flux provide resistance and temperature data. The heat flux is then recovered from inverse theory and compared with the known input heat flux. For the nickel-based sensor, the effect of the film thickness and film overlap with the insulator are investigated. Simulations with box and square function heat input demonstrate the dependence of the sensor frequency response on the film thickness. For the silver thin-film gauge, the effect of partial direct heat transfer into the surrounding insulator is investigated. The suitability of the silver thin film for time-resolved heat flux measurements in a turbulent high-speed boundary layer is evaluated. The unsteady wall heat flux is obtained from a large-eddy simulation of a high-enthalpy Mach 5 turbulent boundary layer in thermochemical nonequilibrium. Inverse analysis of the temperature data from the thin-film simulation provides the wall heat flux, which is in good agreement with the heat flux obtained directly from the large-eddy simulation, thus demonstrating that the thin-film gauge is well suited for impulse facility experiments.