Effect of Rarefaction on Thermal and Chemical Non-Equilibrium for Hypersonic Flow With Different Enthalpy and Catalytic Wall Conditions

Compressibility and rarefaction effect plays an essential role in the design and study of objects experiencing hypersonic flows. The presence of chemical and thermal non-equilibrium in hypersonic flows increases the complexity of estimating aerothermodynamic properties, which are essential for developing thermal protection systems and the aerothermodynamic design of hypersonic vehicles. In this study, the hy2Foam solver, developed in an OpenFOAM framework by hyStrath group, is used to understand the effect of Knudsen number (which in turn depends on the altitude) and freestream enthalpy variation on the surface aerothermodynamic properties such as pressure, heat flux, velocity slip, temperature jump, and flow field variables such as species concentration and temperature, in five-species air flow over a cylinder, for both noncatalytic and fully catalytic wall conditions. The novelty of the work lies in reporting the effect of rarefaction on thermal and chemical non-equilibrium (associated with hypersonic flows), and thus on the surface properties under different enthalpy and wall catalytic conditions. It has been shown that the rarefaction effect is more pronounced on the vibrational temperature component and for high enthalpy gas. The surface wall heat flux and the chemical reaction rate among the species decrease with rarefaction. The skin friction coefficient is one of the most sensitive properties, while the pressure coefficient has been the least susceptible to non-equilibrium effects. The stagnation points heat flux at different Knudsen numbers shows good agreement with the existing correlation in literature for both low and high enthalpy flows, which further establishes the validity of the study done in this work.