Abstract
A series of numerical simulations about tunnel fires are carried out to study the performance of different arrangements of natural ventilation shafts in a 500 m tunnel. Two to four identical shafts are arranged in a group at the centerline and the sideline of the tunnel ceiling. The characteristics of the temperature distribution, velocity field and the total amount of smoke exhausted from each shaft group are investigated for each arrangement. The results have shown that when the fire heat release rate is 20 MW, boundary layer separation occurs in all the shafts in the series of simulations. At the same fire heat release rate, when the number of shafts, n, is ≤ 2, the smoke exhaust performance of the shaft groups arranged on the centerline of the tunnel ceiling is better than that on the sideline of the tunnel ceiling while n is >2, the shaft groups arranged on the sideline have a better overall smoke exhaust performance. The Richardson number of 1.4 proposed by Ji et al. is still applicable to determine the flow phenomena between boundary layer separation and plug-holing.
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