Investigation of Chemical Non-equilibrium Hypersonic Flows in Carbon Dioxide–Nitrogen Atmospheres Using a Coupled Euler–Boundary-Layer Method

Abstract

Re-entry flights in carbon dioxide–nitrogen atmospheres such as Mars and Venus became more and more the focal point of interest in the research community lately. During these re-entry flights at hypersonic velocities, a high-enthalpy flow field is generated behind the bow shock. Due to this high-enthalpy flow field, the constituent chemical species inside this field undergo several significant real gas effects, for example, dissociation. With respect to typical re-entry trajectories starting at high altitudes, low density/low pressure regions are passed during re-entry flights, whereby dissociation occurs at a wide range, starting at relatively low gas temperatures affecting aspects like surface chemistry or wall heat fluxes significantly. Therefore it is important to generate accurate thermodynamic, kinetic and transport models with a chemical non-equilibrium approach, where the conservation equations for momentum, total energy and balance equations are solved for each species in the dissociated flow field. Due to the fact that plasma and shock tunnels are subject to several shortcomings, the importance of efficient numerical simulations is still steadily increasing. Furthermore the Navier–Stokes equations, which are still the most comprehensive equations for continuum fluid dynamics, simultaneously are the most computational costly ones. Therefore the usage of an efficient and accurate numerical approach, which is less general, but generates the same order of accuracy in its domain of application, like the coupled Euler–second-order boundary-layer method, is very promising. As long as there are no strong interactions between the viscous and the inviscid flow, the method described here generates analogous flow physics compared to the Navier–Stokes solutions. Also it already proved its good agreements with numerical simulations of the Navier–Stokes solutions for blunt re-entry bodies at high angles of attack and medium to low altitudes.