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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 ?. The Buoyant Plume. Conditions for a Fire Storm.

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Fire Storms and Large Scale Modelling

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  1. 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

  2. Fire Storms ?

  3. The Buoyant Plume

  4. 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)

  5. Atmospheric Turbulence

  6. Turbulent Explosion

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

  8. Cellular Laminar Explosion

  9. = (ns/nl)D-2 Laminar Instability Inner and Outer Cut-offs Flame area ratio = (ns/nl)D-2 Fractal Dimension, D = 7/3

  10. Spillage Magnitudes

  11. Atmospheric Turbulence

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

  13. Regime of Peak Turbulence-Instability Interaction

  14. Influence of ls/lG on U Masr = 3 Masr = -23

  15. Estimated Donnellson Burning Velocity

  16. Ufa X

  17. Ufa Topography

  18. Ufa Ignition Source

  19. The Buoyant Plume

  20. Ufa Topography

  21. Ufa and Donnellson Burning Velocities Compared

  22. Congestion:Flame and Shock Wave in a Duct a Flame Shock wave A 23

  23. The Maximum Turbulent Burning Velocity

  24. Maximum Turbulent Burning Velocity

  25. Influence of Venting Ratio, A/a

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

  27. 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.

  28. 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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