Low pressure schlieren imaging of 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. Mixing of three flows was examined, 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. From previous planar laser induced fluorescence images it was concluded that small starletted cylinders exhibited the highest degree of mixing, as the starlets created large-scale structures that helped to entrain the flows into one another. Starlets also improved the mixing of large cylindrical ejectors, but not as efficiently as was the case for the small starletted cylinders. Thus, the small starlets effectively maximized both the diffusive and convective aspects of fluid mixing. In this study, schlieren imaging techniques were employed to determine and document the properties and structure of the supersonic flow, yielding descriptive images of the barrel-shaped shocks, expansion waves, and other supersonic flow features at low pressures between 6.6 and 17.5 torr.