Abstract Ambient wind often affects the smoke movement and natural smoke exhaust performance in enclosure fires. In this study, six wind speeds and twelve kinds of vent combinations are designed. 72 groups of experiments are conducted to investigate the coupling effects of vent combination and ambient wind speed during quasi-steady state of natural smoke extraction in chamber fires. Compared to the traditional Particle Image Velocimetry (PIV) method, a novel particle image flow field visualization (PIFFV) technique is proposed, and a smoke recognition algorithm for the determination of smoke layer height is developed based on two-dimensional OTSU method. Experimental results show that using the PIFFV method and the proposed algorithm, smoke layer height can be determined more accurately, in comparison to the N-percentage method. When the height of outlet is higher than that of inlet, the worst smoke control effect is found. When the air inlet is located on the windward side, the effect of natural smoke extraction is better under a reasonable wind speed than that in a windless condition. However, when the height of outlet is lower than that of the windward inlet, the optimal smoke control effect is achieved without ambient wind. In addition, when the inlet is arranged on the sideward side, ambient wind has a limited influence on smoke layer height with a lower outlet. Results of this study can provide references for the design of smoke control and ventilation system in room fires.

中文翻译：

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自然排烟条件下环境风对室内火灾烟层高度影响的可视化研究

摘要 环境风往往会影响围护结构火灾中的烟气运动和自然排烟性能。本研究设计了六种风速和十二种通风口组合。开展了72组实验，研究了室内火灾自然排烟准稳态下通风口组合与环境风速的耦合效应。与传统的粒子图像测速（PIV）方法相比，提出了一种新颖的粒子图像流场可视化（PIFFV）技术，并基于二维OTSU方法开发了一种用于确定烟层高度的烟雾识别算法。实验结果表明，与N-percentage方法相比，使用PIFFV方法和提出的算法，可以更准确地确定烟层高度。当出口高度高于入口高度时，发现控烟效果最差。当进风口位于迎风侧时，在合理风速下自然排烟的效果比无风时更好。但是，当出口高度低于迎风入口高度时，在无环境风的情况下达到最佳控烟效果。此外，当入口布置在侧边时，环境风对烟层高度的影响有限，出口较低。本研究结果可为室内火灾排烟通风系统的设计提供参考。自然排烟的效果在合理风速下比无风条件下更好。但是，当出口高度低于迎风入口高度时，在无环境风的情况下达到最佳控烟效果。此外，当入口布置在侧边时，环境风对烟层高度的影响有限，出口较低。本研究结果可为室内火灾排烟通风系统的设计提供参考。自然排烟的效果在合理风速下比无风条件下更好。但是，当出口高度低于迎风入口高度时，在无环境风的情况下达到最佳控烟效果。此外，当入口布置在侧边时，环境风对烟层高度的影响有限，出口较低。本研究结果可为室内火灾排烟通风系统的设计提供参考。