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Flow, Turbulence and Combustion

, Volume 83, Issue 2, pp 269–292 | Cite as

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

  • Jeffrey M. BergthorsonEmail author
  • Michael B. Johnson
  • Aristides M. Bonanos
  • Michael Slessor
  • Wei-Jen Su
  • Paul E. Dimotakis
Article

Abstract

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.

Keywords

Turbulence Mixing Backward-facing step Shear layer Recirculation 

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Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Jeffrey M. Bergthorson
    • 1
    • 2
    Email author
  • Michael B. Johnson
    • 1
  • Aristides M. Bonanos
    • 1
  • Michael Slessor
    • 1
  • Wei-Jen Su
    • 1
  • Paul E. Dimotakis
    • 1
  1. 1.Graduate Aeronautical LaboratoriesCalifornia Institute of TechnologyPasadenaUSA
  2. 2.Department of Mechanical EngineeringMcGill UniversityMontrealCanada

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