Thermal Characteristics of Air in the Problem of Hypersonic Motion of Bodies in the Earth’s Atmosphere

Abstract

Introduction. The air fl ow around bodies moving in the atmosphere with hypersonic velocities is accompanied by a sharp increase in the air temperature due to the high energy of the fl ow and its dissipation in strong shock waves (SW) characteristic of such fl ows [1]. As the velocity of motion increases, there is an increase in the air temperature behind the shock wave, which leads to the initiation of a number of high-temperature processes such as vibrational excitation of molecules and their dissociation and the formation of molecular and atomic ions. These physicochemical processes have their own relaxation times. When these times are much longer than the characteristic time of the change in the fl ow parameter (in the stationary fl ow the above situation is equivalent to a relaxation length larger than the linear size), the thermodynamical properties of air can be described in the ideal gas approximation with a constant adiabatic index. In the opposite case of a short relaxation time, the thermal parameters of the medium can be assumed to be in equilibrium. To describe the intermediate region where the times are comparable, it is necessary to use physical and chemical kinetics equations [2]. It is known that the above high-temperature processes can not only infl uence locally the fl ow parameters, but also determine its character in general. Nevertheless, considering the hypersonic fl ow without account for the nonequilibrium processes is justifi ed [3], since it permits forming an approximate hydrodynamic fl ow pattern. The present paper gives the results of calculations of the equilibrium properties of a high-temperature air and describes a model of the processes of physicochemical kinetics, which, along with the gas dynamics equations, forms the basis for simulating the hypersonic motion of bodies in the Earth’s atmosphere. Equilibrium Characteristics of Air. In the ideal gas approximation, the system of gas-dynamic equations is closed by the equation of state