RECONSTRUCTION OF FIRE WHIRLS USING SCALE MODELS

This work was motivated from the knowledge of a historical fire whirl accident in which a fire whirl was responsible for 38,000 deaths and serious damage to the environment, all of which happened within 15 minutes. To understand the general features of fire whirls, records of example fire whirls were collected and deduced to be of three different types. Scaling laws were derived using dimensional analysis; three types of scale-models, with scaling ratios of 1/235, 1/2500, and 1/4837, corresponding to three whirls (prototypes), were designed in the laboratory. Wind tunnel fire experiments were performed burning methanol as the fire source and by changing the wind velocity to understand conditions under which fire whirls can occur. The model fire whirls reconstructed in the laboratory were visualized with water vapor; and profiles of velocity and temperature were, respectively, measured by a hot wire anemometer and a fine thermocouple. Because the dynamic structure of prototype fire whirls is not known due to lack of direct measurements in actual flows, a large scale-model with scaling ratio of 1/100 to the prototype was designed to be studied in an open field. This model consisted of 85 circular pans filled with 2.3 m3 of methanol that were distributed in an area of 400 m2. Air movement was visualized by colored smoke. Wind velocity and direction were measured at five different locations and air temperatures at nine different locations. It was found that the visually determined whirl diameter and whirl column height, and the maximum tangential velocity of the whirl can be correlated to the 1/2500 scale model by the proposed scaling laws.