Fire storms and large scale modelling
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Fire Storms and Large Scale Modelling. Derek Bradley University of Leeds UKELG 50TH ANNIVERSARY DISCUSSION MEETING “Explosion Safety – Assessment and Challenges” 9th to 11th July 2013 Cardiff University. Fire Storms ?. The Buoyant Plume. Conditions for a Fire Storm.

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Fire Storms and Large Scale Modelling

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Fire Storms and Large Scale Modelling

Derek Bradley

University of Leeds

UKELG 50TH ANNIVERSARY DISCUSSION MEETING

“Explosion Safety – Assessment and Challenges”

9th to 11th July 2013

Cardiff University


Fire Storms ?


The Buoyant Plume


Conditions for a Fire Storm

High column of burned gas

Large spillage and favourable topology

Turbulence generation at base

Rich aerosol mixture topped by lighter fractions

Large turbulent length scales

(Turbulence, buoyancy and aerosols give positive feed-back)


Atmospheric Turbulence


Turbulent Explosion


Turbulent Burning CorrelationU = ut /u'K =0.25(u'/uℓ)2Rl-0.5


Cellular Laminar Explosion


= (ns/nl)D-2

Laminar Instability Inner and Outer Cut-offs

Flame area ratio

= (ns/nl)D-2

Fractal Dimension,

D = 7/3


Spillage Magnitudes


Atmospheric Turbulence


Turbulent Burning CorrelationU = ut/u'K =0.25(u'/uℓ)2Rl-0.5


Regime of Peak Turbulence-Instability Interaction


Influence of ls/lG on U

Masr = 3

Masr = -23


Estimated Donnellson Burning Velocity


Ufa

X


Ufa Topography


Ufa Ignition Source


The Buoyant Plume


Ufa Topography


Ufa and Donnellson Burning Velocities Compared


Congestion:Flame and Shock Wave in a Duct

a

Flame

Shock wave

A

23


The Maximum Turbulent Burning Velocity


Maximum Turbulent Burning Velocity


Influence of Venting Ratio, A/a


Strong, Stable, Detonations require Low (ξε), or (τi /τe)


Problems of Large Scale Modelling

  • Uncertain discharge composition, mixing, and circumstances of ignition.

  • Uncertain physico-chemical data (Ma, extinction stretch rates, burning velocities, (τi /τe).

  • Complexity of congestions,venting, shock wave reflection and refraction.

  • Uncertainties in rate of change of heat release rate.


References

  • G.M. Makhviladze, S.E. Yakush, (2002) “Large Scale Unconfined Fires and Explosions,” Proceedings of the Combustion Institute 29: 195-210.

  • D. Bradley, M. Lawes, K. Liu, M.S. Mansour, (2013) “Measurements and Correlations of Turbulent Burning Velocities over Wide Ranges of Fuels and Elevated Pressures,” Proceedings of the Combustion Institute 34: 1519-1526.

  • D. Bradley, M. Lawes, Kexin Liu, (2008) “Turbulent flame speeds in ducts and the deflagration/detonation transition,” Combust. Flame 154 96-108.

  • D. Bradley, (2012) “Autoignitions and detonations in engines and ducts,” Philosophical Transactions of the Royal Society a-Mathematical Physical and Engineering Sciences, 370, no. 1960: 689–714.


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