Real Gas Laminar Boundary-Layer Separation Prediction Methodology

Abstract

AREAL gas laminar boundary-layer separation methodology has been developed to predict Space Shuttle Orbiter control surface effectiveness during atmospheric entry. The methodology is based on the LeesKlineberg moment integral theory. A real gas laminar boundary-layer model, having a binary atomic diffusion of frozen gas composition, is assumed. A brief discussion of theory and sample results are presented herein. A set of boundary-layer profile parameters which are required for this theory is given in the full paper. Contents The aerodynamic control surface effectiveness of the Space Shuttle Orbiter (SSO) during re-entry is strongly affected by the laminar flow separation induced by the compressively deflected surface. The SSO re-entry hypersonic control surface effectiveness (HCSE) estimates were initially based primarily on wind-tunnel test data. Extrapolation of test data to higher elevon/body flap deflections revealed that a potential control reversal phenomena may exist. However, the quality of test data was such that a definite control reversal trend could not be established. A methodology for predicting the supersonic/hypersonic laminar boundary-layer separation for the ideal gas case has been developed and presented in Ref. 1. During re-entry, in the flight regime where aerodynamic forces become significant, inviscid air on the windward side of the SSO can be fully dissociated by compression heating. However, since the outer surface skin temperature of the SSO thermal protection system (TPS) will not exceed 2000 K, the neighboring dissociated air will recombine fully. Therefore, a dissociation-recombination cycle of the reacting gas is expected to be produced within the boundary layer, the contribution of which to the laminar flow separation mechanism is presently unknown. Theory for Real Gas Flow Separation Prediction The real gas flow separation prediction methodology, which is suitable for design applications, is derived from the ideal gas Lees-Klineberg Moment Integral Theory.2 Since the analysis of multispecies gas having a finite reaction rate is too complex and not suitable for the integral theory method, an idealized binary reacting gas (molecule-atom of one species of gas) has been selected to represent the approximate behavior of a real gas. The binary-single-species reaction assumption is valid, because in the flight regime considered, one species of molecule is reacting while the others are in an equilibrium