Integrated scramjet nozzle/afterbody performance analysis

Abstract

A two-dimensiona l flowfield computer program developed for preliminary performance analysis of integrated scramjets is presented. Scramjet flowfields are computed by means of the shock-capture technique, with real gas thermodynamic properties for frozen and equilibrium compositions. The program computes internal and external flowfields with multiple shock interactions. Interaction of the exhaust (underexpanded or overexpanded) with the external stream and vehicle afterbody also is considered. Forces and moments are computed due to stream thrust and external surface pressure distributions. Typical program results for parametric nozzle/afterbody design and off-nominal performance analysis are presented. N recent years, increased attention has been given to the application of supersonic combustion ramjets (scramjets) to airbreathing launch vehicles, advanced civil aviation, and hypersonic research aircraft. One of the scramjet technology areas requiring particular attention is the interaction of the airbreathing propulsion system with the vehicle aerodynamics and the resulting effects on the overall vehicle performance. Particularly significant and as yet not well defined is the interaction of the vehicle afterbody and the exhaust of the integrated scramjet.M The integrated scramjet propulsion system utilizes the vehicle afterbody as an extension of the nozzle, producing increased effective exhaust velocities and thrust at the expense of incurred trim penalties. Therefore, a requirement exists for the means to define accurately scramjet nozzle/afterbody exhaust flowfields. A critical review of this problem indicated that detailed analysis should include consideration of real gas three-dimensional flowfields with chemical-kinetic effects, multiple shocks, heat transfer, boundary layer growth, and interaction with the inviscid flow. In view of the complexity of the problem, simplified practical methods of analysis must be developed which retain the most essential features of the flow phenomena, fulfill preliminary design requirements, and produce realistic results. At the present time, the computer programs of Refs. 5 and 6 appear to be the only published programs specifically developed to meet this requirement. These programs consider inviscid and adiabatic quasi-three-dimensional flowfields with real gas equilibrium hydrogen-air chemistry. These programs are based on the reference plane technique, with a table lookup thermodynamic properties routine. This paper represents a simpler scramjet flowfield analysis computer program suitable for preliminary design analyses. Since the majority of the current scramjet configurations are of the modular quasi-two-dimensional type, it is felt that for preliminary design .purposes the flowfield can be described sufficiently well by means of a two-dimensional program. The two-dimensional scramjet flowfield program7 considers inviscid and adiabatic supersonic flow in ducts and coflowing dissimilar streams with real or ideal gas properties. The methodology used in this program is the shock capture technique (SCT) described in Refs. 8 and 9. Thermodynamic properties are evaluated by means of a special-purpose sub