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

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

Fire Storms ?


The buoyant plume

The Buoyant Plume


Conditions for a fire storm

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

Atmospheric Turbulence


Turbulent explosion

Turbulent Explosion


Turbulent burning correlation u u t u k 0 25 u u 2 r l 0 5

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


Cellular laminar explosion

Cellular Laminar Explosion


Laminar instability inner and outer cut offs

= (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

Spillage Magnitudes


Atmospheric turbulence1

Atmospheric Turbulence


Turbulent burning correlation u u t u k 0 25 u u 2 r l 0 51

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


Regime of peak turbulence instability interaction

Regime of Peak Turbulence-Instability Interaction


Influence of l s l g on u

Influence of ls/lG on U

Masr = 3

Masr = -23


Estimated donnellson burning velocity

Estimated Donnellson Burning Velocity


Fire storms and large scale modelling

Ufa

X


Ufa topography

Ufa Topography


Ufa ignition source

Ufa Ignition Source


The buoyant plume1

The Buoyant Plume


Ufa topography1

Ufa Topography


Ufa and donnellson burning velocities compared

Ufa and Donnellson Burning Velocities Compared


Congestion flame and shock wave in a duct

Congestion:Flame and Shock Wave in a Duct

a

Flame

Shock wave

A

23


The maximum turbulent burning velocity

The Maximum Turbulent Burning Velocity


Maximum turbulent burning velocity

Maximum Turbulent Burning Velocity


Influence of venting ratio a a

Influence of Venting Ratio, A/a


Fire storms and large scale modelling

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


Problems of large scale modelling

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

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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