Effects of heat release on turbulent shear flows. Part 3. Buoyancy effects due to heat release in jets and plumes

Francisco Diez Garias, Werner J.A. Dahm

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

An integral method is presented for determining effects of buoyancy due to heat release on the properties of reacting jets and plumes. This method avoids the Morton entrainment hypothesis entirely, and thus removes the ad hoc 'entrainment modelling' required in most other integral approaches. We develop the integral equation for the local centreline velocity uc(x), which allows modelling in terms of the local flow width δ(x). In both the momentum-dominated jet limit and buoyancy-dominated plume limit, dimensional arguments show δ(x) ∼ x, and experimental data show the proportionality factor cδ to remain constant between these limits. The entrainment modelling required in traditional integral methods is thus replaced by the observed constant cδ value in the present method. In non-reacting buoyant jets, this new integral approach provides an exact solution for uc(x) that shows excellent agreement with experimental data, and gives simple expressions for the virtual origins of jets, plumes and buoyant jets. In the exothermically reacting case, the constant cδ value gives an expression for the buoyancy flux (x) that allows the integral equation for uc(x) to be solved for arbitrary exit conditions. The resulting uc(x) determines the local mass, momentum and buoyancy fluxes throughout the flow, as well as the centreline mixture fraction ζc(x) and thus the flame length L. The latter provides the proper parameters Ω and Λ that determine buoyancy effects on the flame, and provides power-law scalings in the momentum-dominated and buoyancy-dominated limits. Comparisons with buoyant flame data show excellent agreement over a wide range of conditions.

Original languageEnglish (US)
Pages (from-to)221-255
Number of pages35
JournalJournal of Fluid Mechanics
Volume575
DOIs
StatePublished - Mar 25 2007

Fingerprint

Shear flow
Buoyancy
buoyancy
shear flow
plumes
heat
entrainment
flames
Momentum
momentum
Integral equations
integral equations
Fluxes
Scaling laws
scaling laws
Hot Temperature

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

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title = "Effects of heat release on turbulent shear flows. Part 3. Buoyancy effects due to heat release in jets and plumes",
abstract = "An integral method is presented for determining effects of buoyancy due to heat release on the properties of reacting jets and plumes. This method avoids the Morton entrainment hypothesis entirely, and thus removes the ad hoc 'entrainment modelling' required in most other integral approaches. We develop the integral equation for the local centreline velocity uc(x), which allows modelling in terms of the local flow width δ(x). In both the momentum-dominated jet limit and buoyancy-dominated plume limit, dimensional arguments show δ(x) ∼ x, and experimental data show the proportionality factor cδ to remain constant between these limits. The entrainment modelling required in traditional integral methods is thus replaced by the observed constant cδ value in the present method. In non-reacting buoyant jets, this new integral approach provides an exact solution for uc(x) that shows excellent agreement with experimental data, and gives simple expressions for the virtual origins of jets, plumes and buoyant jets. In the exothermically reacting case, the constant cδ value gives an expression for the buoyancy flux (x) that allows the integral equation for uc(x) to be solved for arbitrary exit conditions. The resulting uc(x) determines the local mass, momentum and buoyancy fluxes throughout the flow, as well as the centreline mixture fraction ζc(x) and thus the flame length L. The latter provides the proper parameters Ω and Λ that determine buoyancy effects on the flame, and provides power-law scalings in the momentum-dominated and buoyancy-dominated limits. Comparisons with buoyant flame data show excellent agreement over a wide range of conditions.",
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Effects of heat release on turbulent shear flows. Part 3. Buoyancy effects due to heat release in jets and plumes. / Diez Garias, Francisco; Dahm, Werner J.A.

In: Journal of Fluid Mechanics, Vol. 575, 25.03.2007, p. 221-255.

Research output: Contribution to journalArticle

TY - JOUR

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AU - Diez Garias, Francisco

AU - Dahm, Werner J.A.

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N2 - An integral method is presented for determining effects of buoyancy due to heat release on the properties of reacting jets and plumes. This method avoids the Morton entrainment hypothesis entirely, and thus removes the ad hoc 'entrainment modelling' required in most other integral approaches. We develop the integral equation for the local centreline velocity uc(x), which allows modelling in terms of the local flow width δ(x). In both the momentum-dominated jet limit and buoyancy-dominated plume limit, dimensional arguments show δ(x) ∼ x, and experimental data show the proportionality factor cδ to remain constant between these limits. The entrainment modelling required in traditional integral methods is thus replaced by the observed constant cδ value in the present method. In non-reacting buoyant jets, this new integral approach provides an exact solution for uc(x) that shows excellent agreement with experimental data, and gives simple expressions for the virtual origins of jets, plumes and buoyant jets. In the exothermically reacting case, the constant cδ value gives an expression for the buoyancy flux (x) that allows the integral equation for uc(x) to be solved for arbitrary exit conditions. The resulting uc(x) determines the local mass, momentum and buoyancy fluxes throughout the flow, as well as the centreline mixture fraction ζc(x) and thus the flame length L. The latter provides the proper parameters Ω and Λ that determine buoyancy effects on the flame, and provides power-law scalings in the momentum-dominated and buoyancy-dominated limits. Comparisons with buoyant flame data show excellent agreement over a wide range of conditions.

AB - An integral method is presented for determining effects of buoyancy due to heat release on the properties of reacting jets and plumes. This method avoids the Morton entrainment hypothesis entirely, and thus removes the ad hoc 'entrainment modelling' required in most other integral approaches. We develop the integral equation for the local centreline velocity uc(x), which allows modelling in terms of the local flow width δ(x). In both the momentum-dominated jet limit and buoyancy-dominated plume limit, dimensional arguments show δ(x) ∼ x, and experimental data show the proportionality factor cδ to remain constant between these limits. The entrainment modelling required in traditional integral methods is thus replaced by the observed constant cδ value in the present method. In non-reacting buoyant jets, this new integral approach provides an exact solution for uc(x) that shows excellent agreement with experimental data, and gives simple expressions for the virtual origins of jets, plumes and buoyant jets. In the exothermically reacting case, the constant cδ value gives an expression for the buoyancy flux (x) that allows the integral equation for uc(x) to be solved for arbitrary exit conditions. The resulting uc(x) determines the local mass, momentum and buoyancy fluxes throughout the flow, as well as the centreline mixture fraction ζc(x) and thus the flame length L. The latter provides the proper parameters Ω and Λ that determine buoyancy effects on the flame, and provides power-law scalings in the momentum-dominated and buoyancy-dominated limits. Comparisons with buoyant flame data show excellent agreement over a wide range of conditions.

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