ASYMPTOTIC DEFECT BOUNDARY-LAYER THEORY APPLIED TO THERMOCHEMICAL NONEQUILIBRIUM HYPERSONIC FLOWS

Viscous flow computations are required to predict the heat flux or the viscous drag on an hypersonic re-entry vehicle. When real gas effects are included, Navier-Stokes computations are very expensive, whereas the use of standard boundary layer approximations does not correctly a ccount for the 'entropy layer swallowing' phenomenon. The purpose of t his paper is to present an extension of a new boundary layer theory, c alled the 'defect approach', to two-dimensional hypersonic flows inclu ding chemical and vibrational non-equilibrium phenomena. This method e nsures a smooth matching of the boundary layer with the inviscid solut ion in hypersonic flows with strong entropy gradients. A new set of fi rst-order boundary layer equations has been derived, using a defect fo rmulation in the viscous region together with a matched asymptotic exp ansions technique. These equations and the associated transport coeffi cient models as well as thermochemical models have been implemented. T he prediction of the flow field around the blunt-cone wind tunnel mode l ELECTRE with non-equilibrium free-stream conditions has been done by solving first the inviscid flow equations and then the first-order de fect boundary layer equations. The numerical simulations of the bounda ry layer how were performed with catalytic and non-catalytic condition s for the chemistry and the vibrational mode. The comparison with Navi er-Stokes computations shows good agreement. The wall heat flux predic tions are compared to experimental measurements carried out during the MSTP campaign in the ONERA F4 wind tunnel facility. The defect approa ch improves the skin friction prediction in comparison with a classica l boundary layer computation.