Studies on buoyancy driven two-directional smoke flow layering length with combination of point extraction and longitudinal ventilation in tunnel fires |
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| Affiliation: | 1. State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, Anhui , China;2. Institute of Disaster Prevention Science and Safety Technology, Central South University, Changsha 230026, Hunan, China;1. Faculty of Urban Construction and Environment Engineering, Chongqing University, Chongqing 400045, PR China;2. Key Laboratory of Three Gorges Reservoir Region’s Eco-Environment, Ministry of Education, Chongqing 400045, PR China;3. National Centre for International Research of Low-carbon and Green Buildings, Chongqing 400045, PR China;4. Department of Civil Engineering, Aalborg University, DK-9000 Aalborg, Denmark;1. Department of Fire Safety Engineering, Southwest Jiaotong University, Chengdu, PR China;2. Department of Civil and Architectural Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong;1. Faculty of Urban Construction and Environmental Engineering, Chongqing University, Chongqing 400045, PR China;2. Key Laboratory of Three Gorges Reservoir Region’s Eco-Environment, Ministry of Education, Chongqing 400045, PR China;3. National Centre for International Research of Low-carbon and Green Buildings, Chongqing 400045, PR China |
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| Abstract: | This paper investigates the buoyancy-driven smoke flow layering length (both upstream and downstream) beneath the ceiling with combination of point extraction and longitudinal ventilation in tunnel fires. A theoretical model is developed based on previous back-laying model with only longitudinal ventilation, with modified actual heat release rate, as well as modified upstream and downstream opposing longitudinal air flow velocities by the induced flow velocity due to point extraction. Experiments are carried out in a reduced scale model tunnel with dimensionless of 72 m×1.5 m×1.3 m. A LPG porous gas burner is used as fire source. The smoke flow layering length both upstream and downstream are identified based on temperature profiles measured along the ceiling, for different experiment conditions. CFD simulations with FDS are also performed for the same scenarios. Results show that with combination of point extraction and longitudinal ventilation, the smoke flow layering length is not symmetric where it is longer downstream than that upstream. The upstream smoke layering length decreases, while the downstream layering length increases with increase in longitudinal ventilation velocity; and they both decrease with increase in point extraction velocity. The predictions by the proposed theoretical model agree well with the measurements and simulation results. |
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| Keywords: | Tunnel fire Point extraction Longitudinal ventilation Smoke flow layering length Model tunnel experiments FDS |
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