Numerical Simulation of the Backlayer Critical Velocity in the Memorial Tunnel Test (MTFVTP)

Road tunnels constitute key elements in the traffic net, especially for the long distance road transportation but also in the large urban areas. Although security preventions have permitted a relatively low index of accidents in tunnels, the analysis of the accidents in road tunnels during the last years shows an increment in both the number of cases and their gravity. In the case of fires, the control of the smoke propagation becomes crucial because the major risk for people is smoke inhalation rather than the direct exposure to the fire itself. Besides, a quick control of the fire requires that the access and evacuation routes are maintained without smoke. However, research in this field has been limited by the difficulties inherent in the problem, and so there are few experimental data available. This paper pursues the study of the control of the smoke propagation in tunnel roads with a longitudinal air stream. The methodology is based on the numerical simulation of the time evolution of the air and smoke flows induced after the onset of localized fires of different magnitude. Specifically, 10, 20, 50 and 100 MW fires were simulated. A general purpose computational fluid dynamics software is used for this investigation, due to its ability to model multi-species three-dimensional unsteady flows. The general purpose of the paper is the refinement and contrast of a numerical procedure for the simulation of fire tunnels with natural and longitudinal ventilation, as the particular case with the most complex and restrictive conditions, and the use of such procedure to study the backlayering phenomenon. The obtained results were compared with the natural and longitudinal ventilation tests of the Memorial Tunnel test as well as with previous studies.