Low pressure PLIF visualization and mixing quantification in a multi-stream injection nozzle

The mechanisms of the mixing between separate flows are of high interest in order to increase the efficiency of processes that rely on well mixed flows, such as combustion. In this paper, Planar Laser Induced Fluorescence (PLIF), in two perpendicular planes, of an Iodine-seeded flow was used to visualize and quantify the mixing of three flows due to its non-intrusive properties, where two of the flows were in an underexpanded state, and the third near-ideally expanded. One of the underexpanded flows served as a driver gas for the mixing of the remaining two streams, and it was the ejector nozzles of this flow whose geometry was examined with the goal of passively enhancing its driving capability of the mixing of the remaining two flows. It was determined that in general, small starletted cylinders exhibited the highest degree of mixing, possibly due to the starlets creating large-scale structures that entrained the flows into one another. The starlets are also in an underexpanded state; this achieved mixing through convective and diffusive methods, respectively. Starlets did appear to improve the mixing of large cylindrical ejectors, but not to the levels of the small starletted cylinders. Thus, the small starlets effectively maximized both the diffusive and convective aspects of supersonic fluid mixing. Quantitative studies of the PLIF images in general reinforced these conclusions.