Physico - Chemical Modelling in Nonequilibrium Hypersonic Flow Around Blunt Bodies

Abstract

The development of new space transportation vehicle requires better knowledge of hypersonic flow around blunt bodies and an accurate prediction of thermal protection system for extremely high temperatures. The complex domain of this hypersonic research program concerns the fully understanding and the control of reentry flowfield. The vehicle flying with high velocity through the upper layers of the atmosphere with low density. A very strong bow shock wave around vehicle is generated and converted the high kinetic energy into internal energy, thus increasing the temperature of the gas. Therefore, shock layer is the site of intensive physico-chemical nonequilibrium processes such as vibrational excitation, dissociation, electronic excitation, even the ionization and radiation phenomena. Under this typical hypersonic condition, air must be considered as a plasma around the vehicle which perturbes traditionally the communication between the vehicle and ground control station because the plasma absorbs radio waves. The computation of such flowfield is a challenging task. The successful conception of such high technology would not have been possible without some knowledge of these thermochemical nonequilibrium phenomena and how they affect the performance of the vehicle. Some of these informations can either be obtained from experimental facilities such as wind tunnel and ballistic range, or large scale fight experiments, and/or numerical simulations. Moreover, small scale laboratory experiments are severely limited by impossible exact simulation of thermo-chemical nonequilibrium flow around a full scale hypersonic vehicle, and flight experiments are too costly to allow their widespread usage. Therefore, much of these aerothermodynamics informations needed to design future hypersonic vehicle will have to come from numerical predictions (the least expensive approach) which is a reasonable alternative after sufficient validations. The numerical simulation of hypersonic flow in thermochemical nonequilibrium past a blunt body presents considerable difficulties for accurate solutions in the stagnation region. The computational results depend on the choice of the thermochemical model and the strategy of resolution. Generally, efforts provided to solve these types of flows have been based on the full coupling between Navier-Stokes equations and the thermochemical phenomena. Many 5