Real-scale CFD simulations of fire in single- and double-track railway tunnels of arched and rectangular shape under different ventilation conditions

Abstract The development of measures to avoid or minimise the destructive effects of fires in tunnels requires a quantitative assessment of the thermal intake of the structure during such incidents. In the underlying work, a typical tunnel-fire scenario is analysed with the help of Computational Fluid Dynamics ( CFD ) in order to predict temperature distributions inside the tunnel which in turn shall be used to assess the structural stability of the concrete lining. The CFD simulations are based on a fire code previously developed within the framework of OpenFOAM. The fire is simulated in an arched single-track, an arched double-track and a rectangular double-track cross-section of real dimensions taking into account two different ventilation velocities (0.5 and 3 m/s). Results are compared in terms of temperature distributions within the cross-section and longitudinal temperature distributions at ceiling level. Except for the temperature distribution within the cross-sections, little difference in results is seen for the two double-track tunnels with the low ventilation velocity (0.5 m/s), whereas higher temperature levels and a faster downstream movement of hot gases are observed in the single-track tunnel. For the high ventilation velocity (3 m/s), temperature levels drop dramatically and flow parameters within the three tunnel cross-sections differ insignificantly. In addition, a comparison of temperature profiles inside the concrete tunnel lining with results of a more detailed 1D calculation is presented. In order to obtain the most accurate temperature profiles, a procedure is suggested, where the 1D heat-conduction equation is solved by using the fluid temperatures from a previous CFD simulation, taking into account the temperature dependency of thermo-physical parameters of concrete and, if necessary, the risk of spalling.

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