Studying the streamlining of a blunted body by a vibrational-nonequilibrium dissociated gas

Abstract

It is usual in the study of the streamlining of bodies by a nonequilibrium flow of dissociated air to assume equilibrium in the translational, rotational, and vibrational degrees of freedom. However, this approximation does not offer the required accuracy, for example, in examining the fast-acting processes that arise in compression shocks. To describe the structure of the flow in this region it thus becomes necessary to make provision for nonequilibrium vibrational relaxation. In the present study we solve the problem of the streamlining of a blunted body by a vibrational~nonequilibrium dissociated gas within the framework of the CVDV model [i, 2] which takes into consideration the relationship between dissociation and the vibrations. Particular attention is devoted to an analysis of the effect that the processes of dissociation and vibrational nonequilibrium have on the thermal loads of a flight vehicle. We have to make a distinction between two typical situations: the streamlining of a body under conditions of free natural flight and the streamlining of a model in an aerodynamic tunnel (AT). If the approaching stream in the first case is in a state of equilibrium, then under the conditions of the tunnel experiment it is vibrationally "frozen in" and exhibits a level of dissociation different from zero [3]. In this particular study we examine the possible methods of simulating the natural conditions of flight in aerodynamic wind tunnels. The progress of the processes of dissociation and vibrational nonequilibrium in the presence of moderate Reynolds numbers was examined in [4] on the basis of a model of a hypersonic shock layer. The cited theoretical data enabled us to ascertain the significant role played by diffusion near the front of the shock wave. However, the mean-energy equation for the relaxation of vibrations that was used there failed to take into consideration the presence of an atomic component in the dissociated gas. In the following we take this effect into consideration. Specific calculations have been carried out for oxygen and nitrogen. i. The Physical Flow Model. The motion of a relaxing gas mixture consisting of atomic and molecular components is described by a system of conservation equations [5]. Let the rotational degrees of molecular freedom be in equilibrium with the translational degrees of freedom, while no such equilibrium exists between the vibrational and translational degrees of freedom. Then the expressions for the rates of diffusionV M and Va, for the velocity q of the heat flux, and for the average internal energy of a unit volume of gas , contained within the system of conservation equations, may be brought to the following form