This paper has analyzed the asymmetric flow effect of fire-induced thermal flow in a horizontal tunnel under the natural ventilation condition by conducting large eddy simulations (LES). The key objective is to reveal...This paper has analyzed the asymmetric flow effect of fire-induced thermal flow in a horizontal tunnel under the natural ventilation condition by conducting large eddy simulations (LES). The key objective is to reveal and to have a better understanding of the asymmetric flow effect caused by the upstream and downstream tunnel length difference. The mechanism behind it can be explained based on the conservation of mass and dynamic force analysis on the smoke and fresh air. The strength of the asymmetric flow effect is characterized by the mass flow rate of the induced longitudinal flow (net mass flow rate of a cross-section). An empirical correlation to predict the induced longitudinal mass flow rate is proposed. Furthermore, the law of smoke and air flow distribution within a horizontal tunnel is established. The proportion of smoke (or air) flowing out (or coming in) through the opening increase (or decrease) linearly with the increasing distance between that opening to the fire location. The variation of the air flow with the longitudinal fire location in a tunnel is more sensitive than the smoke flow. Results have shown that as the fire approaches the tunnel exit from the middle of the tunnel, the smoke spilling out through this opening is reduced from 50% to 40%, while the fresh air incoming from this opening is increased from 50% to 100% and vice versa.展开更多
Ceiling gas temperature rise is an important evaluation indicator determining the level of risk in a subway tunnel fire.However,very little literature has been found that has addressed the emergency when a fired subwa...Ceiling gas temperature rise is an important evaluation indicator determining the level of risk in a subway tunnel fire.However,very little literature has been found that has addressed the emergency when a fired subway train with lateral multiple openings stops in the interval tunnel.Hence,a battery of full-scale numerical simulations were employed to address the impact of train fire location on the gas temperature beneath the train ceiling.Numerical results showed that the ceiling gas temperature rise is affected by the pressure difference on both sides of fire source and the backflow from the end wall,which depends on the heat release rate and the fire location.The ceiling gas temperature rise decays exponentially in the process of longitudinal spread,and it can be predicted by a dimensionless model with a sum of two exponential equations.Finally,based on a critical fire location(L'cr=0.667),two exponential equations were developed to quantitatively express the influences of the fire size and the fire location on the maximum ceiling gas temperature.The research results can be utilized for providing an initial understanding of the smoke propagation in a subway train fire.展开更多
基金This work was supported by the National Natural Science Foundation of China(NSFC)under Grant No.52006210 and No.51722605and the Key Research and Development Program of Anhui Province under Grant No.201904a07020059The computational resources used in this work were provided by the Supercomputing Environment of Chinese Academy of Sciences(ScGrid).
文摘This paper has analyzed the asymmetric flow effect of fire-induced thermal flow in a horizontal tunnel under the natural ventilation condition by conducting large eddy simulations (LES). The key objective is to reveal and to have a better understanding of the asymmetric flow effect caused by the upstream and downstream tunnel length difference. The mechanism behind it can be explained based on the conservation of mass and dynamic force analysis on the smoke and fresh air. The strength of the asymmetric flow effect is characterized by the mass flow rate of the induced longitudinal flow (net mass flow rate of a cross-section). An empirical correlation to predict the induced longitudinal mass flow rate is proposed. Furthermore, the law of smoke and air flow distribution within a horizontal tunnel is established. The proportion of smoke (or air) flowing out (or coming in) through the opening increase (or decrease) linearly with the increasing distance between that opening to the fire location. The variation of the air flow with the longitudinal fire location in a tunnel is more sensitive than the smoke flow. Results have shown that as the fire approaches the tunnel exit from the middle of the tunnel, the smoke spilling out through this opening is reduced from 50% to 40%, while the fresh air incoming from this opening is increased from 50% to 100% and vice versa.
基金This work was supported by the National Key Research and Development Program of China(No.2018YFC0807600)the National Natural Science Foundation of China(No.51776192),the Youth Innovation Promotion Association CAS(No.CX2320007001)the Fundamental Research Funds for the Central Universities(No.WK2320000048).
文摘Ceiling gas temperature rise is an important evaluation indicator determining the level of risk in a subway tunnel fire.However,very little literature has been found that has addressed the emergency when a fired subway train with lateral multiple openings stops in the interval tunnel.Hence,a battery of full-scale numerical simulations were employed to address the impact of train fire location on the gas temperature beneath the train ceiling.Numerical results showed that the ceiling gas temperature rise is affected by the pressure difference on both sides of fire source and the backflow from the end wall,which depends on the heat release rate and the fire location.The ceiling gas temperature rise decays exponentially in the process of longitudinal spread,and it can be predicted by a dimensionless model with a sum of two exponential equations.Finally,based on a critical fire location(L'cr=0.667),two exponential equations were developed to quantitatively express the influences of the fire size and the fire location on the maximum ceiling gas temperature.The research results can be utilized for providing an initial understanding of the smoke propagation in a subway train fire.
