Fire whirls has been observed to occur during forest, urban and building fires. Under the extreme condition caused by The Great Kanto Earthquake that struck the downtown Tokyo area in 1923, a fire whirl is responsible for 38,000 deaths. To investigate what caused them, historical record of fire whirls were collected and categorized into three types: Tokyo-earthquake type fire whirl, Hamburg-type fire whirl and Dessens-type fire whirl [1]. A series of wind tunnel fire whirl experiments were conducted using laboratory scale models to study specific wind and fire-intensity conditions for each type. In addition, a 1/100-scale model of Tokyo-earthquake type fire whirl was designed at a landfill off the Tokyo Bay for a filed test. This field test successfully reconstructed Tokyo-earthquake type fire whirl, and the measured maximum spinning velocity was found to correlate well with that of the same type laboratory size fire whirl by Froude number scaling law.

     Because of the fluid dynamic structure of the above three types of fire whirls is very complex, they may not be ideal for analytical and numerical studies. Emmons and Ying [2] used a rotating disc surrounded by a fine mesh screen and placed a small pool fire at the center of the disc. The pool fire produced the buoyancy-driven upward flow and fresh air entered the compartment through the screen that was rotating with the table generating swirl motion in the compartment. Recently Battaglia et al. [3,4] numerically simulated the behavior of fire plumes arising from this Emmons type fire whirl by imposing circulation while maintaining a constant heat release rate. Saito and Cremers [5] used two vertically oriented rectangular screens to create a small compartment with a slit in each end. At the center of the compratment floor, a small pool fire generated upward buoyancy flow and fresh air entered the compartment through the slits generating swirl motion in the compartment. A fire whirl created by this apparatus will be called as the fixed frame type fire whirl. Despite those efforts, we still do not completely understand the detailed fluid dynamic structure of any of the above type fire whirls, due to the lack of experimental data on detailed velocity profiles of fire whirls. Therefore, recently we conducted a series of PIV measurements for both Emmons type and the fixed frame type fire whirls.

     This presentation summarizes the Tokyo-earthquake fire whirl disaster and recent progress on PIV velocity profiles for both Emons type and fixed-frame type fire whirls.

References:

1. Soma, S. and Saito, K., Combustion and Flame, 86: 269-284 (1991).
2. Emmons, H.W. and Ying, S. J., Eleventh Symposium (International) on Combustion, 1967, pp. 475-488.
3. Battaglia, F, Rehm, R G, and Baum, H R, Physics of Fluids, 12: 2859-2867 (2000).
4. Battaglia, F, McGrattan, K B, Rehm, R G, and Baum, H R, Combustion Theory and Modeling, 4: 123-138 (2000).
5. Saito, K. and Cremers, C.J., Proc. Joint ASME/JSME Fluid Engineering Conference, Hilton Head, 1995.