The effects of Damköhler number in a turbulent shear layer

Mungal, M. G.; Frieler, C. E.

doi:10.1016/0010-2180(88)90102-2

Cited by 48 publications

(14 citation statements)

References 8 publications

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“…One flow geometry that can produce efficient mixing between two streams is the shear or mixing layer [5][6][7][8][9][10][11][12][13][14][15][16]. The geometry can be tailored to mitigate pressure gradients in the flow and minimize total-pressure losses.…”

Section: Introductionmentioning

confidence: 99%

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

Bergthorson

Johnson

Bonanos

et al. 2009

Flow Turbulence Combust

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The mixing and flowfield of a complex geometry, similar to a rearwardfacing 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 freeshear 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.

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Section: Introductionmentioning

confidence: 99%

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

Bergthorson

Johnson

Bonanos

et al. 2009

Flow Turbulence Combust

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show abstract

“…A characteristic mixing time, r mix , may be calculated as the time of flight of a particle traveling from the nozzle to the downstream location where the shear layer reaches the axis of symmetry. A characteristic chemical time, T che m, may be calculated in a similar manner as used by Mungal and Frieler (1988), given the mean nozzle species and AIAA 98-3618 ambient conditions. As the altitude is increased, T chem will increase due to falling reactant concentrations.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of Afterburning Cessation Mechanisms in Fuel Rich Rocket Exhaust Plumes

Calhoon¹,

.²

1998

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Publicfeporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense. Washington Headquarters Services. Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2. REPORT TYPE A computational study was conducted to identify fundamental physical processes governing the cessation or shutdown of the afterburning of fuel rich rocket exhaust with the atmosphere. Several mechanisms that have been proposed were examined which are: 1) a relaminarization phenomenon, 2) a Damköhler number effect and 3) a classical flame extinction mechanism. Analysis of the simulation results revealed the relammanzation mechanism to be implausible while the Damköhler number effect and the flame extinction mechanisms were found to be valid. The extinction mechanism was also found to dramatically alter the emissions characteristics • and enhance the shutdown behavior which has important implications with respect to radiative heat transfer to the body and missile intercept systems. This is a significant finding because strain rate induced extinction is a previously unrecognized phenomena occurring in rocket exhaust plumes during afterburning cessation. Technical Papers

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“…Another mechanism discussed in Section 1 which may be responsible for afterburning Tchem, may be calculated in a similar manner as used by Mungal and Frieler, 16 given the mean nozzle species and ambient conditions. As the altitude is increased, r chem will increase due to falling reactant concentrations.…”

Section: Computational Methodologymentioning

confidence: 99%

Computational Assessment of Afterburning Cessation Mechanisms in Fuel Rich Rocket Exhaust Plumes

Calhoon¹,

.²

1998

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A computational study was conducted to identify fundamental physical processes governing the cessation or shutdown of the afterburning of fuel rich rocket exhaust with the atmosphere. Several mechanisms were examined which are: 1) a relaminarization phenomenon, 2) a Damköhler number effect and 3) a classical flame extinction mechanism. Analysis of the simulation results revealed the relaminarization mechanism to be implausible while the Damköhler number effect and the flame extinction mechanisms were found to be valid. The extinction mechanism was also found to dramatically alter the emission characteristics and enhance the shutdown behavior which has important implications with respect to radiative heat transfer to the body and missile defense systems. This is a significant finding because strain rate induced extinction is a previously unrecognized phenomena occurring in rocket Approved for public release; distribution unlimited exhaust plumes during afterburning cessation.

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The effects of Damköhler number in a turbulent shear layer

Cited by 48 publications

References 8 publications

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

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

Evaluation of Afterburning Cessation Mechanisms in Fuel Rich Rocket Exhaust Plumes

Computational Assessment of Afterburning Cessation Mechanisms in Fuel Rich Rocket Exhaust Plumes

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