Unexpected heat flux augmentation in a free-piston high-enthalpy shock tunnel (HIEST) was numerically analyzed. Since a previous experimental study implied that the radiation heating from the shock layer caused the augmentation, a three-dimensional thermochemical non-equilibrium CFD code including radiation transport calculation in the shock layer was developed. This calculation was conducted under the following models: 1) Radiation heating from the air species in the shock layer was calculated by a solving radiative transport equation using tangent slab approximation; and 2) Radiation heating from impurities such as carbon soot and metal particulates, which could be included in the upstream test gas, was calculated by assuming the shock layer as a grey body with averaged shock layer temperature for a trial calculation. The calculations were performed at the stagnation enthalpy and stagnation pressure from 7 to 21 MJ/kg and 31 to 55 MPa, respectively. For air species radiation, radiative heat flux was too small to contribute heat flux augmentation. On the other hand, for grey body assumption, we could find that abnormal heat flux augmentation could be expected by ε σ Tave4
for an engineering technique, where ε
denotes the emissivity ε
= 0.132 and Tave4
was the average shock layer temperature.
View full abstract