Effects of Buoyancy and Forcing on Transitioning and Turbulent - - PDF document

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Effects of Buoyancy and Forcing on Transitioning and Turbulent - - PDF document

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Effects of Buoyancy and Forcing on Transitioning and Turbulent Circular Jet Flames Joseph W. Nichols, James J. Riley, Peter J. Schmid University of Washington Nov. 24, 2003 Supported by the NASA Microgravity Research Division Outline

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SLIDE 1

Effects of Buoyancy and Forcing on Transitioning and Turbulent Circular Jet Flames

Joseph W. Nichols, James J. Riley, Peter J. Schmid University of Washington

  • Nov. 24, 2003

Supported by the NASA Microgravity Research Division

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SLIDE 2

Outline

  • Numerical Method
  • Axisymmetric Simulations

– Parametric study – 3D instabilities not captured

  • Fully 3D Simulations

– Enhanced instability – Flow visualizations reveal 3D structure of instabilities

  • Linear Stability Analysis

c 2003 Joseph W. Nichols 1

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SLIDE 3

Round Fuel Jet

Lateral Collar x r θ Inlet Outlet u0 d

Figure 1: Computational Domain

c 2003 Joseph W. Nichols 2

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SLIDE 4

Numerical Method

  • Compressible Navier-Stokes with

Low Mach Number Approximation (McMurtry et al.)

  • One step, Arrhenius-type reaction
  • Predictor-Corrector scheme (Najm

et al.) handles large density ratios

  • Staggered 6th order compact

schemes

  • Centerline treated with asymptotic

expansions (Constantinescu et al.)

c 2003 Joseph W. Nichols 3

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SLIDE 5

Axisymmetric Simulations

Figure 2: Density contours, Fr =

u0 √gd c 2003 Joseph W. Nichols 4

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SLIDE 6

Buoyancy Effects

  • Buoyancy produces instability
  • Disturbance source

– Round-off – Outlet pressure fluctuations

  • Slightly buoyant and non-buoyant

flames differ significantly (Bahadori et al.) – Perturbation magnitudes – 3D instabilities

c 2003 Joseph W. Nichols 5

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SLIDE 7

3D DNS: Normal gravity

Figure 3: Temperature, Fr = 5

c 2003 Joseph W. Nichols 6

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SLIDE 8

3D DNS: Zero gravity

Figure 4: Temperature, Fr = ∞

c 2003 Joseph W. Nichols 7

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SLIDE 9

Linear Stability Analysis

  • Guides an understanding of

instabilities

  • Linearized low Mach number

equations

  • Parallel mean flow ¯

ux(r), ¯ T(r)

  • Primitive variable formulation
  • Spatially growing disturbances

ω ∈ R, α ∈ C (1)

c 2003 Joseph W. Nichols 8

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SLIDE 10

Eigenvalue Spectrum

Figure 5: Spatial eigenvalues

c 2003 Joseph W. Nichols 9

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SLIDE 11

Conclusions

  • Buoyancy greatly enhances

instability in circular jet flames

  • Buoyant instabilities are highly

three dimensional

  • Introducing buoyancy into the

linear stability problem produces additional instability modes

c 2003 Joseph W. Nichols 10