CFD Simulation of Thermal Plume and Firebrands Scattering in Urban Fire

Abstract

Firebrands are found to be an important factor in the spread of large urban fire. In this study, the scattering of firebrands in an urban fire was numerically simulated by means of CFD (Computational Fluid Dynamics). Firstly, the thermal plume of the urban fire is predicted using a modified compressible k-ε turbulent model. Then a Lagrangian trajectory model that incorporated forces due to the drag, pressure, and gravity force of the firebrands is applied to predict the trajectory of the firebrands. The influences of the inflow wind velocity, diameter, generating site, and initial generating velocity were investigated. It is found that when the inflow wind velocity is comparatively low, the thermal plume is significant, and when the inflow wind is strong, the thermal plume is suppressed. It is shown that the lighter the mass of the firebrand is, the farther the firebrand may be scattered. The stronger the fire's thermal plume is, the higher it may be scattered. More firebrands can be scattered out of firing building by increasing the initial generating velocity.