Boundary layer separation of lateral concentrated smoke exhaust with multi-group separating exhaust vents in tunnel fires under its influencing factors

Abstract Boundary layer separation (BLS) unavoidably occurs in lateral concentrated smoke exhaust (LCSE) systems with multi-group separating exhaust vents during tunnel fires, which consequently reduces smoke exhaust efficiency. It is essential to identify the factors influencing BLS, characterize its variation law, and quantify its scale. In this study, BLS occurrence is determined using the critical criteria of flow velocity, and the volume of each BLS region is employed to quantify its scale. A dimensionless functional relationship between BLS and influencing factors is established through numerical simulation. The variation law of BLS is analyzed from two perspectives: that of the individual exhaust vent and that of the overall exhaust system, elucidating the coupling mechanisms of multiple influencing factors. The findings demonstrate that the scale of BLS can be expressed as multivariate exponential functions of dimensionless parameters representing the exhaust volume, width-height ratio, setting height, and spacing of the exhaust vent. BLS within the exhaust vent is influenced more strongly by both the exhaust vent parameters and the exhaust strategy than BLS within the exhaust duct. Moreover, the influence of the exhaust vent parameters surpasses the exhaust strategy. Optimizing the setting height and width-height ratio of the exhaust vent is therefore key to mitigating BLS. This study provides guidance for optimizing the design of LCSE systems with multi-group separating exhaust vents to enhance smoke exhaust efficiency.