Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage t...Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage to the surrounding area. Numerical simulations of a lab-scale flame that simulates a fire whirl were performed to investigate the changes in gas temperature and velocity fields under various fuel inflow velocities. The flow field was obtained by solving a continuity equation and a three-dimensional Navier-Stokes equation, and the turbulence was resolved using a large eddy simulation. A chemical equilibrium partially premixed combustion model was used, and radiation effects were considered. The time-averaged gas temperature distribution along the burner central axis revealed that the gas temperature decreased monotonically from upstream to downstream. The time-averaged velocity distribution along the burner central axis showed that the velocity decreased as one moved downstream, but the decrease was uneven. The time variation of the gas temperature demonstrated that the higher the fuel inflow velocity, especially near the burner, the greater the gas temperature flutter. Furthermore, the larger the fuel inflow velocity, the larger the flame swell and wobble. The results showed that the fuel inflow velocity affected temperature fluctuation and flame undulating movement.展开更多
Numerical studies on internal fire whirls(IFW)generated in a vertical shaft model with a single corner gap were reported in this paper.The generation of IFW,burning rate of fuel and temperature were studied experiment...Numerical studies on internal fire whirls(IFW)generated in a vertical shaft model with a single corner gap were reported in this paper.The generation of IFW,burning rate of fuel and temperature were studied experimentally first.Numerical simulations on medium-scale IFW were carried out using a fully-coupled large eddy simulation incorporating subgrid scale turbulence and a fire source with heat release rates compiled from experimental results.Typical transient flame shape was studied and then simulated numerically by using temperature.The dynamic phenomena of generation and development of IFW were simulated and then compared with experimental results.The predicted results were validated by comparing with experimental data,which demonstrated that an IFW can be simulated by Computational Fluid Dynamics.Numerical results for flame surface,temperature,and flame length agreed well with the experimental results.The IFW flame region and intermittent region were longer than those for an ordinary pool fire.The modified empirical formula for centerline temperature was derived.Variations of vertical and tangential velocity in axial and radial directions were also shown.The vortex core radius was found to be determined by the fuel bed size.Velocity field was not measured extensively due to resources limitation.Comparing measured temperature distribution with predictions is acceptable because temperature is related to the heat release rate,air flow and pressure gradient.展开更多
文摘Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage to the surrounding area. Numerical simulations of a lab-scale flame that simulates a fire whirl were performed to investigate the changes in gas temperature and velocity fields under various fuel inflow velocities. The flow field was obtained by solving a continuity equation and a three-dimensional Navier-Stokes equation, and the turbulence was resolved using a large eddy simulation. A chemical equilibrium partially premixed combustion model was used, and radiation effects were considered. The time-averaged gas temperature distribution along the burner central axis revealed that the gas temperature decreased monotonically from upstream to downstream. The time-averaged velocity distribution along the burner central axis showed that the velocity decreased as one moved downstream, but the decrease was uneven. The time variation of the gas temperature demonstrated that the higher the fuel inflow velocity, especially near the burner, the greater the gas temperature flutter. Furthermore, the larger the fuel inflow velocity, the larger the flame swell and wobble. The results showed that the fuel inflow velocity affected temperature fluctuation and flame undulating movement.
基金sponsored by the National Natural Science Foundation of China(No.11402061)The work described in this paper was also partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region,China,for the project“A study on electric and magnetic effects associated with an internal fire whirl in a vertical shaft”(Project No.PolyU 15206215)with account number B-Q47D.
文摘Numerical studies on internal fire whirls(IFW)generated in a vertical shaft model with a single corner gap were reported in this paper.The generation of IFW,burning rate of fuel and temperature were studied experimentally first.Numerical simulations on medium-scale IFW were carried out using a fully-coupled large eddy simulation incorporating subgrid scale turbulence and a fire source with heat release rates compiled from experimental results.Typical transient flame shape was studied and then simulated numerically by using temperature.The dynamic phenomena of generation and development of IFW were simulated and then compared with experimental results.The predicted results were validated by comparing with experimental data,which demonstrated that an IFW can be simulated by Computational Fluid Dynamics.Numerical results for flame surface,temperature,and flame length agreed well with the experimental results.The IFW flame region and intermittent region were longer than those for an ordinary pool fire.The modified empirical formula for centerline temperature was derived.Variations of vertical and tangential velocity in axial and radial directions were also shown.The vortex core radius was found to be determined by the fuel bed size.Velocity field was not measured extensively due to resources limitation.Comparing measured temperature distribution with predictions is acceptable because temperature is related to the heat release rate,air flow and pressure gradient.
