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Mixing Measurements in a Supersonic Expansion-Ramp Combustor

Bonanos, Aristides M. and Bergthorson, Jeffrey M. and Dimotakis, Paul E. (2008) Mixing Measurements in a Supersonic Expansion-Ramp Combustor. Flow, Turbulence and Combustion, 80 (4). pp. 489-506. ISSN 1386-6184. doi:10.1007/s10494-008-9133-7.

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This paper reports results on molecular mixing for injection via an expansion-ramp into a supersonic freestream with M_1 = 1.5. This geometry produces a compressible turbulent shear layer between an upper, high-speed “air” stream and a lower, low-speed “fuel” stream, injected through an expansion-ramp at α = 30° to the high-speed freestream. Mass injection is chosen to force the shear layer to attach to the lower guide wall. This results in part of the flow being directed upstream, forming a recirculation zone. Employing the hypergolic hydrogen-fluorine chemical reaction and pairs of “flip” experiments, molecular mixing is quantified by measuring the resulting temperature rise. Initial experiments established the fast-chemistry limit for this flow in terms of a Damköhler number (Da). For Da ≥ 1.4, molecularly mixed fluid effectively reacts to completion. Parameters varied in these experiments were the measurement station location, the injection velocity of the (lower) “fuel” stream, the stoichiometry for the flip experiments, and the density ratio of the fuel and air streams. As expected, mixing increases with increasing distance from the injection surface. The mixed fluid fraction increases by 12% when changing the fuel-to-air stream density ratio from 1 to 0.2. Comparisons with measurements at subsonic (high-speed) “air” stream velocities show that the trend of decreasing mixing with increasing speed documented in free-shear layer flows is also encountered in these flows. The current geometry produces higher mixing levels than do free shear layers.

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Additional Information:© 2008 Springer. Received: 17 July 2007 / Accepted: 3 January 2008. The authors would like to acknowledge constructive discussions with C. Bond and G. Matheou. D. Lang assisted with the computers and electronics associated with the facility control and data acquisition. The experiments were conducted with the expert assistance of E. Dahl. This work was funded by the AFOSR under Grants FA9550-04-1-0020 and FA9550-04-1-0389, whose support is gratefully acknowledged.
Funding AgencyGrant Number
Air Force Office of Scientific Research (AFOSR)FA9550-04-1-0020
Air Force Office of Scientific Research (AFOSR)FA9550-04-1-0389
Subject Keywords:Molecular mixing, Compressible turbulent shear layer, Supersonic combustion
Issue or Number:4
Record Number:CaltechAUTHORS:20160602-161703534
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67599
Deposited By: Paul Dimotakis
Deposited On:13 Jun 2016 22:20
Last Modified:11 Nov 2021 03:51

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