A simplified model of fires in road tunnels. Comparison with three-dimensional models and full-scale measurements

Abstract

A new simplified model (UPMTUNNEL) for the simulation of accidental fires in road tunnels with longitudinal ventilation is presented. The model follows a mixed approach, and has characteristics typical of both field and zone models. Like field models, the proposed model calculates the main properties at every point in the whole domain. The tunnel is divided in two zones: the plume, located upstream from the point at which the smoke hits the ceiling, and a diffusion zone extending downstream. Each of these two regions is analyzed assuming steady-state conditions. The plume is described by one-dimensional conservation equations for turbulent flows. To deduce the 1D equations, the 3D problem is considered to be parabolic along the center-line of the flame, and self-similar profiles in planes normal to this line are assumed. The diffusion region is studied as an incompressible unidirectional problem, described by the energy conservation equation. 3D models and full-scale experiments have been used in order to validate the results of the UPMTUNNEL model. Two different general-purpose codes are employed: FLUENT and PHOENICS, in which the eddy break-up and k– ε– g turbulent combustion models have been, respectively, implemented.