Basic investigation of fluid-acoustic interactions in a supersonic rectangular jet ejector

摘要

The internal mixing region of a small-scale supersonic rectangular jet ejector was experimentally investigated. A rectangular converging-diverging nozzle (AR=4) with a design Mach number of 1.5 issues into a constant-area rectangular duct. A physically realistic duct-to-jet area ratio of 2 was used for all experiments, resulting in secondary fluid entrainments approaching M2=0.6 Particle Image Velocimetry (PIV), flow visualization, and surface pressure measurements were used to study the internal characteristics of the ejector flow-field. Substantial mixing increases were observed when the most unstable Strouhal frequency of the unheated primary jet is matched with a transverse duct mode of the ejector. This self-excitation resulted in the production of large-scale structures between the primary and secondary streams. Specifically, the presence of this effect in an unheated case resulted in a 13 increase in secondary mas entrainment and thrust augmentation above the expected performance trends. With the exception of the self-excited case, the growth rates of the internal mixing layers agree very well with published planar mixing-layer data. This indicates that the strong static pressure gradient in the duct has a negligible effect on mixing. However, the growth rate of the self-excited mixing layer exceeded the growth rate measured in a planar free shear layer by over 50 (measured at identical convective Mach numbers). Finally, the primary jet was heated to 650 K to study the temperature effects on internal mixing and performance. The increased density and velocity ratio in the heated case resulted in improved mixing, fluid entrainment, and thrust augmentation.