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A high-performance smoke exhaust system is vital for maintaining a tenable environment during fire accidents evacuation. This study proposes a novel vortex flow driven smoke exhaust system to delay the smoke filling process during the atrium fire accident. The complex fluid movement and combustion reactions were predicted using Fire Dynamics Simulator, and the predicted smoke filling process was identified by the least-square method. Good agreements between numerical predictions and experimental measurements for vertical temperature, tangential velocity profile and smoke interface height were achieved. The numerical outcomes revealed that the amount of fresh air supplied, heat release rate and exhaust fan's rate determined the smoke interface's final height. A parametric study was also carried out to investigate the dominating factor in maintaining a stable vortex flow to maximize the smoke exhaust efficiency. Numerical results showed that the vortex flow smoke exhaust system could slow down the smoke filling, and the stability of the swirling fire is crucial for the system's performance.

-Fire whirl is a rotating fire with either a fixed or revolving flame centre-core caused by unbalanced entrainment. In general, the flame height of a fire whirl is significantly larger than that of a free standing fire. It is suggested by several studies that fire whirl is a disastrous scenario especially in urban or bush fires since it can greatly promote the fire spread and escalate the thread to human lives and species. In this paper, as a preliminary study, the fire whirl behaviour has been studied numerically using the Fire Dynamics Simulator (FDS) ver 6.1.2 which is based on the large eddy simulation (LES). It incorporates the mixture fraction based combustion model along with soot formation, the subgrid-scale (SGS) turbulence model, radiation transfer equation (RTE) model which are fully coupled and interactive. This allows the modelling of all essential chemical and physical behaviours that occur during the fire whirling processes. A small-scale vertical shaft with a base of 0.34 m × 0.35 m with a total vertical height of 1.45 m is considered. The development stages including the ignition, flame-rising and fully-developed fire whirling are modelled successfully through numerical simulations. Fairly good agreements between simulation and experimental results for temperature profiles at the centreline and corner thermocouples are achieved. However, a flame height of 0.3 m to 0.4 m is estimated in the simulation while the experimental observation is around 0.6 m. Also, the temperature is slightly over-predicted at the centre while under-predicted at the corner. These could well be due to the simplified chemistry employed in the FDS. With this preliminary numerical study, it could be logically inferred that the detailed chemical reactions scheme may be needed to capture the fundamental governing characteristics of the fire whirl in future numerical modelling studies.

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The Wall Adpating Local Eddy Viscosity (WALE) subgrid-scale turbulence model was adopted for an in-house large eddy simulation (LES) fire code in which the turbulence is fully coupled combustion and radiation models. The traditional Smagorinsky subgrid-scale model accounts only strain rate of the turbulent structure while the WALE model considers both the strain and the rotation rates. Furthermore, the WALE model automatically recovers the near wall-scaling for the eddy viscosity hence more adaptive for wall bounded flows.A 15 m long test hall fire was reconstructed by the in-house fire code with 1.5 MW fire source. The performance of the WALE model was assessed by comparingpredicted transient gas temperatures and velocities at various spatial locations.