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 

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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

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ORGANIZED FLOW

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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.