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Large Eddy Simulations (LES) of smoke extraction duct system (SEDS) in single compartments of different volumes (i.e., 128 m 3 , 512 m 3 and 2400 m 3 ) with FDS 6.5.3 are presented. The required grid resolution for accurate flow inside the duct systems is discussed and the influence of different SEDS design parameters (i.e., shape and position of duct system, number and position of extraction openings) on the smoke extraction efficiency of the system is analysed. The extraction rates applied to the SEDS are determined a-priori based on simplified calculations with these estimates compared against the predicted CFD results (i.e., in terms of predicted smoke free heights inside the compartments). Overall, the numerical predictions are satisfactory (i.e., within less than 5 % errors) in most of the scenarios considered, apart from the 2400 m 3 compartments, where the smoke free heights are 20 % lower than expected. The analysis of the numerical simulation results reveals some important aspects, including that the use of multiple extraction openings is not efficient, in terms of smoke extraction, in the same duct of the same compartment and that the local velocities, at the level of the extraction openings, can potentially exceed the maximum allowed design values. Among the SEDS design parameters, the position and shape of the duct (i.e., rectangular or flat) as well as the position of the extraction opening(s) do not have a significant influence in terms of predicted smoke free heights. [ABSTRACT FROM AUTHOR]

Investigations of ventilation in an immersed tunnel have recently drawn greater research attentions; however, analyses on the influence of vent design and tunnel width on ventilation performance have rarely been addressed. For the sake of the security of evacuees in an immersed tunnel fire, the influence of three vent designs and two immersed tunnel widths on mechanical ventilation performance during tunnel fires were numerically investigated using large eddy simulation. The pollutant gas flow characteristics in the tunnel after a fire were analyzed, and the pollutant gas exhaust efficiency based on the mass conservation of carbon monoxide in the smoke was proposed in this study. By comparing the smoke propagation, smoke distribution, and exhaust efficiency between three different vent designs, it was determined that the Top Vent Design has the best smoke exhaust effect, and the Sidewall Vent Design (with an activated vertical smoke screen) has a better smoke exhaust effect than the Sidewall Vent Design. The influences of the tunnel width and heat release rate of the fire on the ventilation effect were also investigated. [ABSTRACT FROM AUTHOR]