Freestream Flow Reconstruction from Heat Flux and Pressure Measurements in a Mach 6 Arcjet Tunnel

Numerical simulations were performed to reconstruct heat flux and pressure measurements obtained in the Mach 6 arc-heated facility at the University of Tennessee, operated with nitrogen flow. In the experiments, stagnation-point heat flux and pitot pressure were measured at a bulk enthalpy of 6.8 MJ/kg and a total pressure of 170 kPa. The heat flux was determined using a flat-nose probe instrumented with a fast-response coaxial thermocouple flush-mounted at the stagnation point, while pitot pressure was measured with a hemispherical-nose probe. The experimental data were originally processed using simplified theoretical relations, such as the Sutton–Graves and Fay–Riddell stagnation heating formulas, to estimate the enthalpy distribution in the hypersonic freestream. In this study, three-dimensional CFD calculations with the open-source code OpenFOAM were employed to reproduce the experiments and reduce uncertainty in the estimated tunnel flow conditions. Best agreement with the measurements was obtained using a total enthalpy of 7.28 MJ/kg for the flat probe, which is about 8% lower than the value inferred from the first-order analysis.