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Published September 2009 | public
Journal Article

Molecular Mixing and Flowfield Measurements in a Recirculating Shear Flow. Part I: Subsonic Flow


The mixing and flowfield of a complex geometry, similar to a rearward-facing step flow but with injection, is studied. A subsonic top-stream is expanded over a perforated ramp at an angle of 30°, through which a secondary stream is injected. The mass flux of the second stream is chosen to be insufficient to provide the entrainment requirements of the shear layer, which, as a consequence, attaches to the lower guidewall. Part of the flow is directed upstream forming a re-entrant jet within the recirculation zone that enhances mixing and flameholding. A control-volume model of the flow is found to be in good agreement with the variation of the overall pressure coefficient of the device with variable mass injection. The flowfield response to changing levels of heat release is also quantified. While increased heat release acts somewhat analogously to increased mass injection, fundamental differences in the flow behaviour are observed. The hypergolic hydrogen-fluorine chemical reaction employed allows the level of molecular mixing in the flow to be inferred. The amount of mixing is found to be higher in the expansion-ramp geometry than in classical free-shear layers. As in free-shear layers, the level of mixing is found to decrease with increasing top-stream velocity. Results for a similar configuration with supersonic flow in the top stream are reported in Part II of this two-part series.

Additional Information

© 2009 Springer. Received: 6 March 2008. Accepted: 2 January 2009. Published online: 3 February 2009. We acknowledge many fruitful discussions with C. Bond, C. Pantano, and G. Matheou. E. Iglesias assisted with several of the experiments. G. Katzenstein provided engineering support, and D. Lang provided essential assistance with the electronics used for facility control and data acquisition. The experiments were made possible through the many contributions of E. Dahl to facility design, maintenance, and safety. This work was funded by AFOSR Grants FA9620-01-1-0006 and FA0550-04-1-0389, whose support is gratefully acknowledged.

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