Aerothermodynamic analysis of hypersonic flows with applications for atmospheric reentry procedures

Abstract

In this project, we will investigate hypersonic flows including effects of thermodynamic non-equilibrium and chemical reactions of dissociation and ionization on the distribution of surface heat flux of reentry capsules. During the atmospheric reentry procedure, strong shock waves are formed around the vehicle enhancing the conversion of gas kinetic energy into thermal energy which is, in turn, transferred to the vehicle surface as heat. Atmospheric reentry involves high-temperature gas mixtures and subsequent dissociation effects of the gas molecules. Depending on the temperature, ionization of the molecular or atomic components present in the mixture may also occur. Furthermore, excitation of internal energy modes of the molecules are certainly bound to occur, leading to a thermodynamic non-equilibrium condition. The accurate prediction of dissociation and ionization effects in numerical simulations of hypersonic flows is of utmost importance for the calculation of the heat flux along the surface of spacecraft and satellites. Several aspects of hypersonic flows involving reentry flows remain open in the literature. In terms of the flow physics, the role of the bulk viscosity coefficient is not fully understood. Most studies devoted to numerical modeling of viscous gas flows have taken into account only the shear viscosity coefficient while the bulk viscosity is usually neglected. Taking into account the bulk viscosity in the flow equations results in a mutually related variation of temperature, concentration of gas mixture, shock layer thickness, and shock wave structure, with all parameters affecting non-equilibrium. The coupling between thermal radiation and convective effects is also a current research topic. Hypersonic vehicles reentering into the Earth's atmosphere lead to flows with dissociated air species. These conditions typically exist behind the strong shock waves that substantially increase the gas temperature and affect operational flight issues related to the thermal protection system. In addition, in cases of more extreme Mach numbers, ionization occurs and affects radar communications. In such cases, radiation has an important role in generating additional heat loads to the vehicle surface with contributions as high as 18% of the convective heat. Finally, numerical aspects of hypersonic flow simulations also remain open in the literature, for example, those with respect to mesh resolution requirements. While recent studies have discussed about such requirements for high-speed inert flows, mesh requirements are not fully understood in simulations of reactive flows. (AU)