Numerical study on wall pressure over cone region of blunt-nosed body in high enthalpy shock tunnel HIEST

A cause of an overestimation of the computed surface pressure on a blunted cone in high-temperature hypersonic flow is explored. The overestimation was observed in a free-piston shock tunnel at the stagnation of H₀ = 15.6 and 10.1 MJ/kg. The sensitivity analysis reveals that a reduction of the upstream translational temperature in the range of 100 to 300 K substantially improves the agreement of the surface pressure with the measured data. As the cause of the lower upstream translational temperature, radiative cooling effect is included in the thermochemical nonequilibrium calculation in the nozzle, the translational temperature at the nozzle exit is reduced to about 250 K. Using the obtained flow variables as the upstream boundary condition, the computed pressure agrees quite well with the experimental data. In order to clarify whether other variables such as translational-vibrational relaxation time, chemical reaction rates, and upstream chemical composition could be the cause of the discrepancy, uncertainty quantification is employed. It is shown that these parameters of the thermochemical model and upstream chemical composition have minor effect on the agreement of surface pressure. It is concluded that the observed discrepancy in the surface pressure is due to radiative cooling effect of high temperature gas in the nozzle region.