Numerical investigation on the characteristics of lateral smoke extraction in the immersed road tunnel

A series of numerical simulations are carried out to explore the characteristics of the smoke layer in an immersed road tunnel with the lateral smoke extraction system. The temperature distribution and velocity field near the lateral exhaust vent with different aspect ratios were investigated, together with the mass flow rate of CO through the lateral exhaust vent. The results show that the smoke layer stratification is quite stable with the lateral smoke extraction, and the plug-holing phenomenon with the exhaust of fresh air from the bottom edge of the lateral exhaust vent is obviously different from that during the traditional ceiling smoke exhaustion process. A relatively smaller exhaust velocity or a larger heat release rate prevents the plug-holing phenomenon effectively. The major streamlines presented a flattened "S" shape through the cross section of the immersed road tunnel. The lateral exhaust vent with a higher aspect ratio shows an inherent disadvantage in smoke exhaustion performance, while a flattened exhaust vent under a larger effective contact area with a smoke layer could remove the smoke gas more effectively. In terms of smoke exhaustion volume and energy-saving, a lateral exhaust vent with an aspect ratio of 1:3 shows optimal smoke exhaustion performance in the immersed road tunnel. The effectiveness of some potential measures to prevent plug-holing and improve lateral smoke exhaustion is validated briefly. These outcomes will provide some basic guidance and references for the future design of lateral smoke exhaust in the road tunnel.