Characteristics of fire smoke density jump downstream of ceiling barrier in tunnels

doi:10.16265/j.cnki.issn1003-3033.2023.02.2639

Abstract

Abstract:

In order to investigate the variation in smoke flow parameters caused by the ceiling barriers and its effects on human evacuation and smoke control system design, brine water experiments were employed to investigate the condition for the occurrence of density jump for the smoke flow downstream of the ceiling barriers and the resulting mass entrainment and smoke layer thickness variation. Results show that the Froude number exceeds one and then drops to be lower than one immediately in the downstream region of the barrier, representing a transition from super-critical to sub-critical flow state, which could be the reason for the occurrence of the density jump of smoke. The smoke density jump leads to the entrainment of fresh air and the smoke layer thickness increase. The height of the ceiling barrier is a crucial parameter influencing the intensity of smoke flow density jump. The ratio of the smoke layer thickness after the density jump and the one before the density jump, the ratio of Froude number before the density jump and one after the density jump and the mass entrainment ratio increase with the increase of dimensionless height of the barrier. When the dimensionless height of the barrier exceeds 0.267, the above three parameters decrease with the increase of the dimensionless height of the barrier. The density jump of smoke flow downstream of the barrier can exceed 0.3, which is larger than the prediction result of the theoretical model.

Key words: tunnel ceiling, barrier, smoke density jump, smoke mass entrainment ratio, brine water experiment

YANG Dong, CHEN Yilei, DU Tao. Characteristics of fire smoke density jump downstream of ceiling barrier in tunnels[J]. China Safety Science Journal, 2023, 33(2): 68-74.

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References 18

[1]	阳东, 李萍. 抑制倾斜隧道烟气流动热压主导模式的临界风压[J]. 中国安全科学学报, 2022, 32(5):41-47. doi: 10.16265/j.cnki.issn1003-3033.2022.05.0938
	YANG Dong, LI Ping. Critical mechanical pressure rise for preventing buoyancy-dominated flow pattern in inclined tunnel fire with longitudinal ventilation[J]. China Safety Science Journal, 2022, 32(5): 41-47. doi: 10.16265/j.cnki.issn1003-3033.2022.05.0938
[2]	杨宇轩, 程辉航, 龙增, 等. 阻塞效应对隧道火灾烟气温度影响试验研究[J]. 中国安全科学学报, 2022, 32(10):135-141. doi: 10.16265/j.cnki.issn1003-3033.2022.10.1792
	YANG Yuxuan, CHENG Huihang, LONG Zeng, et al. Experimental study on effect of blockage on smoke temperature in tunnel fire[J]. China Safety Science Journal, 2022, 32(10): 135-141. doi: 10.16265/j.cnki.issn1003-3033.2022.10.1792
[3]	ZHANG Shaogang, HUANG Yilong, SHI Long, et al. A fly-wing smoke screen to improve the smoke exhaustion performance of a vertical shaft in road tunnel[J]. Tunnelling and Underground Space Technology, 2021, 113:DOI:10.1016/j.tust.2021.103983. doi: 10.1016/j.tust.2021.103983
[4]	郑梓德, 侯龙飞. 自动挡烟垂壁对隧道火灾的控制研究[J]. 安全与环境工程, 2011, 18(5): 69- 73.
	ZHENG Zide, HOU Longfei. Study on the effect of automatic smoke screen on tunnel fire[J]. Safety and Environmental Engineering, 2011, 18(5): 69- 73.
[5]	GB 51251—2017, 建筑防烟排烟系统技术标准[S].
	GB 51251-2017, Technical standard for smoke management systems in buildings[S].
[6]	WILKINSON D L, WOOD I R. A rapidly varied flow phenomenon in a two-layer flow[J]. Journal of Fluid Mechanic, 1971, 47(2): 241-256.
[7]	MEHROTRA S C. An alternative formulation of the problem of density jump[J]. Tellus, 1974, 26(5): 579-581.
[8]	EZHOVA E V, ZILITINKEVITCH S S, RVBUSHKINA G V, et al. On the application of a turbulence closure modified model to the description of the density jump evolution in a stably stratified medium[J]. Izvestiya Atmospheric and Oceanic Physics, 2016, 52(3): 294-300. doi: 10.1134/S0001433816030038
[9]	DELICHATSIOS M A. The flow of fire gases under a beamed ceiling[J]. Combustion and Flame, 1981, 43(1): 1-10. doi: 10.1016/0010-2180(81)90002-X
[10]	REGEV A, HASSID S, POREH M. Density jumps in smoke flow along horizontal ceilings[J]. Fire Safety Journal, 2004, 39(6): 465-479. doi: 10.1016/j.firesaf.2004.04.002
[11]	REGEV A, HASSID S, POREH M. Calculation of entrainment in density jumps[J]. Environmental Fluid Mechanics, 2006, 6 (5): 407-424. doi: 10.1007/s10652-006-9000-9
[12]	QU Liang, CHOW Wanki. Numerical studies on density jump in a long corridor fire[J]. Tunnelling and Underground Space Technology, 2012, 32: 113-126. doi: 10.1016/j.tust.2012.05.007
[13]	XI Yanhong, CHOW Wanki, MAO Jun. Aerodynamics simulation on density jump in a long corridor fire[J]. Tunnelling and Underground Space Technology, 2015, 50: 23-31. doi: 10.1016/j.tust.2015.06.008
[14]	HUANG Jinlei, ZHU Guoqing, YU Mengwei, et al. Effect of smoke barrier in narrow space on smoke flow utilizing CFD[J]. Procedia Engineering, 2016, 135:142-150. doi: 10.1016/j.proeng.2016.01.095
[15]	POREH M, MARSHALL N R, REGEV A. Entrainment by adhered two-dimensional plumes[J]. Fire Safety Journal, 2008, 43(5): 344-350. doi: 10.1016/j.firesaf.2007.11.001
[16]	YANG Dong, DING Yao, DU Tao, et al. Buoyant back-layering and the critical condition for preventing back-layering fluid in inclined tunnels under natural ventilation: brine water experiments[J]. Experimental Thermal and Fluid Science, 2018, 90:319-329. doi: 10.1016/j.expthermflusci.2017.08.015
[17]	DU Tao, YANG Dong, WEI Haibin, et al. Propagation and entrainment of buoyancy-driven flows in a narrow horizontal space and implications for buoyant contaminant transport under natural ventilation[J]. Building and Environment, 2018, 132:214-224. doi: 10.1016/j.buildenv.2018.02.001
[18]	LINDEN F P. The fluid mechanics of natural ventilation[J]. Annual Review of Fluid Mechanics, 1999, 31(1):201-238. doi: 10.1146/fluid.1999.31.issue-1

工况序号	b/mm	Q_e,0/ (cm²·s^-1)	B_e,0/ (cm³·s^-3)	厚度/mm			弗劳德数			ε
工况序号	b/mm	Q_e,0/ (cm²·s^-1)	B_e,0/ (cm³·s^-3)	h₄	h₁	h₂	Fr₄	Fr₁	Fr₂	ε
1	0	1.48	105.38	18	18	17	0.7	0.7	0.7	—
2		3.05	217.16	20	20	20	0.7	0.7	0.7	—
3		4.64	330.37	24	23	23	0.7	0.8	0.7	—
4	4	1.48	105.38	24	14	20	0.7	1.3	0.8	0.11
5		3.05	217.16	27	18	23	0.6	1.2	0.7	0.14
6		4.64	330.37	33	24	27	0.6	1.1	0.7	0.16
7	8	1.48	105.38	24	8	17	0.7	1..8	1.0	0.23
8		3.05	217.16	27	9	18	0.6	1.8	0.9	0.23
9		4.64	330.37	36	15	25	0.6	1.6	0.8	0.23
工况序号	b/mm	Q_e,0/ (cm²·s^-1)	B_e,0/ (cm³·s^-3)	厚度/mm			弗劳德数			ε
工况序号	b/mm	Q_e,0/ (cm²·s^-1)	B_e,0/ (cm³·s^-3)	h₄	h₁	h₂	Fr₄	Fr₁	Fr₂	ε
10	12	1.48	105.38	28	6	16	0.5	2.1	1.0	0.29
11		3.05	217.16	33	7	20	0.5	1.9	0.7	0.29
12		4.64	330.37	39	12	26	0.5	1.7	0.7	0.25
13	16	1.48	105.38	34	5	15	0.4	2.5	1.0	0.33
14		3.05	217.16	36	6	17	0.4	2.5	0.9	0.31
15		4.64	330.37	41	8	21	0.3	1.9	0.7	0.30
16	20	1.48	105.38	36	3	11	0.3	2.3	1.2	0.32
17		3.05	217.16	41	5	19	0.3	1.6	0.7	0.29
18		4.64	330.37	47	7	23	0.3	1.7	0.7	0.28