Heat flux anomaly in high-enthalpy and high reynolds number flow

The series of aerodynamic heating test campaigns with blunt shaped models in hypersonic high-enthalpy flow were conducted in JAXA-HIEST. Four different blunt shaped models were applied in this study; Apollo CM 6.4% scale model, HRV capsule 6% scaled model and two hemi-sphere probes with radius of curvature r=20mm and r=100mm. Numerical analysis with an axis-symmetric Navier-Stokes thermo-chemical non-equilibrium code was also conducted. Stagnation pressure was almost fixed to P₀=50MPa, while stagnation enthalpy was varied from H₀=7MJ/kg to 21MJ/kg. The unit Reynolds number under the condition was 0.9million/m to 3million/m and the boundary layer was hence mainly fully laminar flow. Abnormal high-heat flux was observed under high enthalpy condition (H₀>10MJ/kg), which anomalies were almost twice higher than those of numerical calculations or theoretical ones. The measurement with four different blunt models showed that the abnormal heat flux was increased as stagnation enthalpy. From the analysis of compression process of the free-piston driver, radiation heating from driver gas does not seem to explain this heating anomaly. The numerical analysis implied that the heating anomaly was related to radiation from unknown atoms or molecules in shock layer.