Nonequilibrium Spectral Radiative Properties Of High Temperature Flow Field Of Hypersonic Vehicles

A strong shock will be formed in the flow field when Aircrafts enter into the atmosphere. Temperature and pressure will be significantly increased behind the shock, resulting in thermochemical nonequilibrium reactions. Radiative effects of hot gases on heat flux on the surface of aircrafts have been very significant. Radiative properties of high temperature flow field are thus required for efficient design of thermal protection systems. thermochemical nonequilibrium gas dynamics and spectral radiative properties in the flow field are researched during reentry into the earth’s atmosphere for RAM_CⅡ detector in this paper. The numerical simulations in this paper adopt Park two-temperature kinetic model to analyze nonequilibrium degree of the whole flow field. And then spectral radiative properties in the flow field behind the shock are solved by line-by-line method.Two-temperature model, as well as multi-temperature model, is the main model in the simulation of nonequilibrium reactive flow field around hypersonic vehicles. The Euler equations considered the conservation of vibrational energy equation are used to solve the distributions of flow field around RAM_CⅡ during reentry into the earth’s atmosphere at the altitudes of 61,71 and 81km above the earth. The nonequilibrium effects are characterized by two-temperature model. The reactive gases considered are respectively 5, 7 and 11 concentrations. The distributions of temperature and component concentration along the stagnation obtained by simulation are in agreement with the results in the literature. The electron number of density obtained is in agreement with the results probed by flight tests. High temperature regions concentrated in the flow field behind the shock around the head of aircrafts. As the altitude increases, the temperature and shock stand-off distance increase, the number density of concentrations decrease. From wall to free flow, the electron number density decrease first and then increase. At the same time, a dimensionless parameter is defined in this paper called noneuilibrium degree, which is used to characterize the degree of noneuilibrium in the whole flow field. The analysis shows that the nonequilibrium degree of thin layer close to the shock, where the noneuilibrium degree is the highest, is up to 0.9.When solving the gas radiative properties, line-by-line method can give highresolution, highly accurate results. Based on data obtained by numerical simulation, spectral radiative properties of hot gases is solved by line-by-line method. The nonequilibrium radiative mechanisms of air plasma are analyzed and researched within 1000-150000cm-1, including bound-bound transitions, bound-free transitions and freefree transitions. The results show that free-to-free transitions and NO infrared electronic system have larger contributions to absorption coefficient in infrared band, separate transitions of N, O, N2 and N2+ have larger contributions to absorption coefficient in the near-infrared and visible band, separate transitions of atomic and photoionization of atomic and diatomic have larger contributions to absorption coefficient.