AI AA - 99 - 3588 Supersonic Coaxial Jet Experiment for CFD Code Validation

A supersonic coaxial jet facility has been designed to provide experimental data suitable for the validation of CFD codes used to analyze high-speed propulsion flows. The center jet is of a light gas and the coflow jet is of air, and the mixing layer between them is compressible. Various methods have been employed in characterizing the jet flow field, including schlieren visualization, pitot, total temperature and gas sampling probe surveying, and RELIEF velocimetry. A NavierStokes code has been used to calculate the nozzle flow field and the results compared to the experiment. INTRODUCTION There is a need for data sets to validate computational fluid dynamics (CFD) codes used to analyze high-speed propulsion flows, such as those in supersonic combustion ramjets (scramjets). Such data sets should have well-defined inlet conditions and flow geometries, and flow fields that have been well documented using a variety of instrumentation. These data sets should also provide a challenging and relevant test of the codes, particularly the empirically-based turbulence models. Previous detailed experimental studies of high speed mixing flows have tended to either concentrate on the simplest case of a two-stream planar mixing layer or on the much more complex problems of injection and mixing (and enhancement of mixing) in a supersonic duct flow. There now exists a large body of work on the two-stream planar mixing layer. Many of these are phenomenological studies intended to gain understanding of the effects of compressibility on mixing Dimotakis’ reviews much of this literature. Some of the cases studied may have been sufficiently well documented for code validation. However, highspeed propulsion flows tend to have only relatively small regions which resemble the two stream planar mixing layer, while in the greater part of an engine mixing occurs between partially mixed fuel-air plumes and “free-stream” air (there being no “core” of unmixed fuel remaining). A number of well documented studies of injection into a supersonic duct flow exist (e.g., Donohue and McDaniel’ ) and these provide excellent test cases, representative of scramjet flows ’. However, such flows are very complex and there is need for detailed data sets in a flow of intermediate complexity. that of a coaxial jet discharging into stagnant laboratory air, with center jet of a light gas (a mixture of 5% oxygen and 95% helium by volume) and coflow jet of air. Both coflow and center-jet nozzles were operated to provide exit flow at 1 atmosphere. The presence of oxygen in the center-jet gas was to allow the use of an oxygen flow-tagging technique (RELW) to obtain non-intrusive velocity measurements in the flow. Both jets are nominally Mach 1.8, but because of the greater speed of sound of the center-jet gas the velocity in the The geometry chosen for the experiment was Associate Professor, Senior Member AIAA tGraduate Research Scholar Assistant, Member AIAA, now at Lockheed Martin Corp., Palmdale, Ca. *Graduate Research Scholar Assistant, Member AIAA, now at Raytheon Corp. Tucson, Az. ‘Research Scientist, Senior Member AIAA ‘Senior Research Scientist, AIAA Associate Fellow ** Copyright