laboratory studies of fire whirls workshop... · alexander j. smits, katie a. hartl, stacy guo and...
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Laboratory Studies of Fire Whirls(preliminary)
Alexander J. Smits, Katie A. Hartl, Stacy Guo and Frederick L. Dryer
Princeton University
Coupled Atmosphere‐Bushfire Modelling Workshop
16‐18 May 2012
High Reynolds number in the lab:compressed air up to 200 atm as the working fluid
Princeton/DARPA/ONR Superpipe:Fully-developed pipe flow ReD = 31 x 103 to 35 x 106
Reτ = up to 106
Reλ = up to 2000
Princeton/ONR Hgh Reynolds number Test Facility: boundary layer flow Reθ = 5 x 103 to 220 x 103
Re⎮ = up to 75,000
Fric & Roshko, 1994; Kelso & Smits, 1995
Fire tornado Kentucky “Bourbon,” Josh Grimes
QuickTime™ and ah264 decompressor
are needed to see this picture.
Examples of Fire Whirls
• Peshtigo Fire, WI – 1871 (>1000 deaths)• Hifukusho-ato, Tokyo – 1923 (~38,000 deaths)• Great Chicago Fire, USA – 1871 • Hiroshima, Dresden Hamburg
• Mann Gulch Fire – 1949 (13 deaths)• Indians Fire, CA – 2008 (4 casualties)• (plume shedding, cold fronts, L-shaped fires)
Laboratory experiments
Emmons and Ying (1967) Byram and Martin (1962)
Rotating screen setup (Emmons and Ying, 1966)
Tangential slit setup (Byram and Martin, 1962)
Previous work
• Emmons and Ying (1966) – rotating frame qualitative
• Byram and Martin (1962) – fixed frame qualitative
• Saito and Cremers (1995) – fixed frame apparatus
• Satoh and Yang (1996) – fixed frame qualitative
• Hassan (2005) – fixed frame quantitative
• Akhmetov (2007) – rotating frame quantitative
• Lei (2011) – fixed frame quantitative
Fire Whirl Principles
Whirls occur:1.ambient vorticity (ground BL, nonuniform horizontal density, earth’s rotation)2.concentrating mechanism (rising air in buoyant column encourages turbulent mixing of gas with vorticity bearing air and transports vorticity aloft)
Devastation occurs:1.rotating core decreases turbulence of rising air (centripetal force)2.ground slows down the rotation of the air and pushes vorticity filled boundary layer towards axis of rotation
Implications:1.buoyancy is not diffused and a large pressure gradient created2.more air and fuel sucked into vortex core
Emmons and Ying (1967)
Order in Chaos
Order in Chaos
Ambient Vorticity
• Boundary Layers
• Non‐uniform density gradients
Concentrating Mechanism
• Centripetal force – vertical pressure gradient
• Ground effects – radial pressure gradient
Types of Fire Whirls
• Kuwana et al. (2007 categorized pool fire whirls into three different types:
• 1) the fire whirl spinning over the downstream-side of the burning area creating a tall fire column
• 2) the fire whirl periodically spinning off from the burning area and traveling to the downstream unburned area
• 3) the relatively stable spinning of air initially without fire in the unburned area but then attracting fires into its spinning motion from the burning area.
Scaling Type 3 Fire whirls
U = wind speed
Uc = critical wind speed
Ub = buoyant velocity at the flame tip
L = horizontal length scale
Γ= circulationH = height of plume
m = burn rate
Kuwana et al. (2007)
(n = 1/4)
• Fuel rich core
• Rankine vortex model outside core
• Solid body rotation inside core
• Order of magnitude decrease in turbulence
• Increased burning rate
• Scaling parameters (air intake velocity, burning rate, flame base size)
• Velocity profile outside
• Velocity profile inside whirl
Known Unknown
• Fuel rich core
• Rankine vortex model outside core
• Solid body rotation inside core
• Order of magnitude decrease in turbulence
• Increased burning rate
• Scaling parameters (air intake velocity, burning rate, flame base size)
• Velocity profile outside
• Velocity profile inside whirl
Even with 50 years of research, the combustion dynamics of fire
whirls is far from being completely clarified, mainly due to a shortage of quantitative
experimental research. (Lei 2011)
Known Unknown
Experimental Setup
• Cylindrical entrainment walls (Plexiglas for PIV)
• Meker burner to generate flame
• LPG fuel: mixture of propane and butane with tank, regulator, needle valve, toggle valve
• Diffusion flame
Lab Made Whirls
Lab Made Whirls
QuickTime™ and a decompressor
are needed to see this picture.
ORGANIZED FLOW
QuickTime™ and a decompressor
are needed to see this picture.
1 in 2 in
3 in 4 in
5 in 6 in
Qualitative Observations
– Stable fire whirls were established using gaseous fuel, diffusion flame structure
– Threshold cylinder size, beyond which it is less important (may be that the outer flow needs some whirl diameters in size to establish)
– Threshold gap size, beyond which it is less important (may be that the mass flow is more or less constant)
– Whirl height depends on fuel flow rate but not strongly
Going Forward
• Short Term:– Velocity profiles using Particle Image Velocimetry (PIV) outside the flame
– Velocity profiles using PIV inside the flame– Impact of fuel burning rate on velocity profiles using PIV
• Long Term:– Understand scaling of “free” fire whirls– Understand fire whirl influence in propagating the fire line
PIV in Fire
• Particles in combusting flows– aluminum oxide, titanium dioxide
(Kompenhas (2001))
– silica (Hassan (2005))
– glass microspheres (Akhmetov (2007))
– smoke particles (Hassan (2005), unspecified function)
• Particle diffusion– Cannot recirculate particles
– Fluidized bed for metal/glass particles (expensive)
• Difficulties– Metal particles in air are hazardous
(sealing, cleaning)
– Expensive metal particle distribution method
– Light emitted from flame – filter to block light from flame and particles (Kompenhas (2001))
• Alternatives– Oil droplets (not in literature for
combusting flames)
– Smoke particles
QUESTIONS?Thank you,
Bibliography
H. W. Emmons and S.J. Ying, “The fire whirl,” in Proceedings of the 11th International Symposium on Combustion, pp.475‐488, Combustion Institute, Pittsburgh, PA, 1967.
G. M. Byram and R.E. Martin, “Fire whirlwinds in the laboratory,” Fire Control Notes, vol. 33, pp. 13‐17, 1962.
K. Satoh and K.T. Yang, “Experimental observations of swirling fires, “Proceedings of the ASME Heat Transfer Division, vol. 4, 1996.
K. Saito and C.J. Cremers, “Fire‐whirl enhanced combustion,” ASME Instructional Fluid Mechanics, vol. 220, 1995.
M.I. Hassan, et al., “Flow structure of a fixed‐frame type fire whirl,” Fire Safety Science Proceedings of the 8th International Symposium, pp. 951‐962, 2005.
D.G. Akhmetov, N.V. Grecov, V.V. Nikulin, “Flow structure in a fire tornado‐like vortex,” Doklady Physics, vol. 52, no. 11, pp. 592‐595, 2007.
J. Lei, et al. “Experimental research on combustion dynamics of medium‐scale fire whirl.” Proceedings of the Combustion Institute 33, pp. 2407‐2415, 2011.
J. Kompenhas, et al. “Application of particle image velocimetry to combustion flows: design considerations and uncertainty assessment,” Experiments in Fluids, vol. 30, pp. 167‐180, 2001.