Flame height of turbulent fire whirls: A model study by concept of turbulence suppression

This paper presents a new semi-physical analysis for the flame height of turbulent fire whirls based on the concept of turbulence suppression. Turbulent fire whirl experiments were performed by a square channel model facility, using propane (30 cm in burner diameter, 25-300 kW in heat release rate) and heptane (15 50 cm in pool size) as representative of gas and liquid fuels, respectively. The Richardson number (Ri), defined by the mean quantities of flow, is used to characterize the turbulence suppression in turbulent fire whirls by the mixing length being represented as a decreasing linear function of Ri. By using the radially-integrated mixture fraction equation and an equation for the radius of fire whirl plume, a flame height correlation is derived which couples the heat release rate, the Richardson number and the axial velocity parameters. The experimental data of propane and heptane fire whirls fit well with the new correlation, which indicates that the correlation can be used to determine the flame heights of fire whirls for different types of fuels. It is demonstrated that the turbulence suppression is the dominant mechanism which controls the flame elongation in turbulent fire whirls compared to free turbulent pool fires of equal fire size. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.