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A procedure for simulating the injection of supercritical ethylene into nitrogen is used to investigate aspects of the injection of supercritical fuels, considered to be an enabling technology in the design of hydrocarbons-fueled scramjet engines. The method solves the compressible Navier-Stokes equations for an ethylene/nitrogen mixture, with the thermodynamic behavior of ethylene described using the Peng-Robinson equation of state. Homogeneous equilibrium and finite-rate phase-transition models are used to describe the growth of a condensed ethylene phase in several axisymmetric and three-dimensional injector nozzles. Predictions are compared with shadowgraph and direct-lighting imaging data, mass flow rate measurements, mole-fraction and temperature measurements in the jet mixing zone, and wall pressure distributions. Qualitative trends relating to jet structure, the appearance of a condensed phase, and the effects of back pressure and injectant temperature are in good agreement with experimental results but indicate the need for improved characterization of the nozzle flow before injection and the inclusion of a better turbulence model for the jet mixing zone. For conditions where both are applicable, a nucleation/ growth phase transition model provides a similar bulk fluid response as a homogeneous equilibrium model but also yields predictions of number density and average droplet size.

§** The dual-mode scramjet engine uses an isolator between the inlet and the combustion chamber to help maintain a stable airflow. A Computational Fluid Dynamics (CFD) model was created based on the isolator test section used at the Air Force Institute of Technology (AFIT). Using the VULCAN CFD code, 2-D results were simulated for inflow Mach numbers of 1.8 and 3. These results will be used later for the development of a 3-D transient model of the isolator.

The U.S. Air Force has long engaged in research concerning scramjet technology, which involves wind-tunnel investigation of vehicles and components intended for flight at Mach numbers between four and eight. As many hypersonic wind tunnels make use of combustion heating, the effects of combustion products on performance must be analyzed and understood. One particular concern is the possibility that water, present as a product of hydrocarbon combustion, will condense as the fluid expands to supersonic conditions, thus altering the thermodynamic environment of the research article. The implementation of homogeneous nucleation theory in a new CFD solver allows the modeling of nucleation, condensation, and later vaporization as they interact with and influence other thermodynamic effects. Use of this solver for axisymmetric nozzle simulations has allowed an exploration of the Mach number / flight condition parameter space for a representative research series, with emphasis on degree and effects of condensation. Results provide guidance on which thermodynamic conditions are likely to produce strong condensation and which are unlikely to be affected. Two-dimensional wedge simulations evaluate the extent to which the increase in static temperature resulting from forebody shocks is likely to vaporize any condensed fluid and return the flow to an ideal state. Degree of vaporization is shown to be a strong function of wedge angle and a weaker function of freestream Mach number and flight condition. Overall results show that, while condensation can be significant under certain conditions, careful selection of thermodynamic parameters can minimize its impact and should allow successful research.

support requirements and volumetric energy density considerations. The engine cycle and fuel choice pose unique challenges related to the jet-in-crossflow problem, and the design of a successful scramjet combustor remains one of the most challenging problems in supersonic aerodynamics. Among the many formidable tasks facing scramjet designers are the injection of fuel without introducing unacceptably large losses, the efficient mixing of the fuel with the freestream (where efficiency must be measured in terms of both time or distance and energy loss), the stabilization of a combustion region, and the management of heat transfer to walls and injector surfaces. Gaseous injection studies have investigated the effects of discharge orifice shapes (circular vs. elliptic), injector configurations (normal vs. angled, cascade, aeroramp), and different injectants (air vs. helium). The injection of pure and aerated liquids into high-speed crossflows has been studied. Liquid injection studies have investigated the fundamental breakup processes of liquid column, spray penetration height, and the effects of injection angle, liquid aeration, and injection conditions on spray structures.

Our purpose in this paper is to present and discuss a tightly integrated and coordinated experimental numerical study of a complex flow. More than that, we hope to show not only the virtues of such an approach in this particular case, but rather to make a strong argument for the proposition that this kind of approach should be the norm, not a rarity. The mere fact that a session on "Computational Adjuncts to Experiments" is considered unusual or necessary at an AIAA meeting clearly suggests that research programs are planned from the outset in this way far too infrequently. The Introduction contains a quote from G.I Taylor that bears directly on the point above. Then, the flow problem of interest here is described. This is gaseous injection from a complex array of nine flushwall, sonic injectors into supersonic flow. The methods and results of the experimental studies are presented next. Then the methods and results of the computational studies are given. Finally, the conclusions reached on the basis of both studies together are discussed.