| The effect of triangular tabbed driving nozzles on the performance of air-air ejectors has been investigated. Testing was performed on a cold-flow wind tunnel. The results of a numerical analysis using a commercially available CFD package have been compared to experimental data. Ejector systems under consideration are intended for installation on gas-turbine engines, where infrared suppression is of interest.; As part of the study, four delta-shaped mixing tabs mounted around the perimeter of a nozzle were positioned through a range of 150°-90°. These tests were compared to baseline cases where tabs were not present. Variations to ejector geometry were also investigated. These included standoff distance, mixing-tube diameter, and mixing-tube length. In addition, testing involved modifications to the mixing tube inlet in an effort to suppress separation at the entrance. Ejectors were evaluated for pumping, mixing, back-pressure, and pressure recovery.; Experimental testing indicated that tabs significantly improved pumping and mixing, but incurred large back-pressure penalties. Variations in ejector geometry were generally shown to have minimal affect on pumping and back-pressure, but in some cases, mixing improved dramatically. In the case of increasing mixing-tube length, greater improvements in mixing were realized with the use of tabs, relative to the baseline case.; The Realizable k-epsilon turbulence model was used for numerical studies. A comparison of CFD to experimental results indicated that CFD models used in this study were capable of predicting experimental trends in the majority of cases, but had difficulty accounting for magnitude. CFD models were capable of predicting a set of counter-rotating vortices generated by each tab, but tended to under predict the magnitude of the streamwise vorticity. CFD is thought to be capable of participating in the design cycle of air-air ejectors provided that its limitations are recognized. |
