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Laboratory Studies of Fire Whirls (Preliminary) 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/ONR Hgh Reynolds number Princeton/DARPA/ONR Superpipe: Test Facility: boundary layer flow Fully-developed pipe flow 3 6 3 3 ReD = 31 x 10 to 35 x 10 Reθ = 5 x 10 to 220 x 10 Re = up to 106 Re⎮ = up to 75,000 τ Reλ = up to 2000 Fric & Roshko, 1994; Kelso & Smits, 1995 QuickTime™ and a h264 decompressor are needed to see this picture. Fire tornado Kentucky “Bourbon,” Josh Grimes 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 Rotating screen setup Tangential slit setup (Emmons and Ying, 1966) (Byram and Martin, 1962) Emmons and Ying (1967) 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 Emmons and Ying (1967) 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 created 2.more air and fuel sucked into vortex core Order in Chaos Order in Chaos Ambient Vorticity Concentrating Mechanism • Boundary Layers • Centripetal force – vertical • Non‐uniform density pressure gradient gradients • 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 (n = 1/4) Uc = critical wind speed Ub = buoyant velocity at the flame tip L = horizontal length scale Γ= circulation Kuwana et al. (2007) H = height of plume m = burn rate Known Unknown • Fuel rich core • Scaling parameters (air • Rankine vortex model intake velocity, burning rate, outside core flame base size) • • Solid body rotation inside Velocity profile outside core • Velocity profile inside whirl • Order of magnitude decrease in turbulence • Increased burning rate Known Unknown • Fuel rich core • Scaling parameters (air • Rankine vortex model intake velocity, burning rate, outside core flame base size) • • Solid body rotation inside Velocity profile outside core • Velocity profile inside whirl • Order of magnitude Even with 50 years of research, decrease in turbulence the combustion dynamics of fire • Increased burning rate whirls is far from being completely clarified, mainly due to a shortage of quantitative experimental research. (Lei 2011) 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 • Difficulties – aluminum oxide, titanium dioxide – Metal particles in air are hazardous (Kompenhas (2001)) (sealing, cleaning) – silica (Hassan (2005)) – Expensive metal particle distribution – glass microspheres (Akhmetov (2007)) method – smoke particles (Hassan (2005), – Light emitted from flame – filter to unspecified function) block light from flame and particles (Kompenhas (2001)) • Particle diffusion • Alternatives – Cannot recirculate particles – Oil droplets (not in literature for – Fluidized bed for metal/glass particles combusting flames) (expensive) – Smoke particles Thank you, QUESTIONS? 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..
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