Experimental study on aerodynamic heat of sphere heads in high enthalpy flow

Vehicles re-entering the Earth's atmosphere with extremely high re-entry velocities face serious aerodynamic heating problems. In order to investigate the thermochemical non-equilibrium phenomenon caused by high enthalpy flow, heat flux measurement experiments and CFD simulations of the spherical head profile have been carried out in the wind tunnel FD-14X, which is a newly constructed high enthalpy expansion wind tunnel of the China Aerodynamic Research and Development Center (CARDC). It has the ability to generate incoming flow with the second cosmic velocity and the total temperature greater than 10 000 K, thus it can produce flows with a total enthalpy up to 70 MJ/kg. In this study, the heat flux measurement on the hemispheres with diameters of 20～50 mm in the flow of a total enthalpy of 16.9～63.5 MJ/kg was carried out, and the flow fields were photographed by self-illumination. CFD simulations of the flow fields around the hemispheres were carried out using the two-temperature non-equilibrium model. The numerical and experimental results show that when the total enthalpy of the incoming flow is greater than 5 MJ/kg, there is a remarkable thermochemical non-equilibrium phenomenon in the flow field around the sphere heads. When the total enthalpy of incoming flow is less than 20 MJ/kg, the wall surface of the 304 steel model shows the noncatalytic characteristic; when the total enthalpy of the incoming flow is greater than 30 MJ/kg, the wall surface of the 304 steel model shows the catalytic characteristic. When the hemisphere surface is coated with a zirconia film and the total enthalpy of the incoming flow is 49.5 MJ/kg, the surface of the model shows the characteristics of a noncatalytic wall.