喷淋与火羽流相互作用的数值模拟

Numerical simulation on interaction of fire plume with sprinkler spray

采用CFD软件FDS,对小室木垛火灾在喷淋情况下火羽流与喷淋的相互作用进行了数值模拟分析,重点比较了喷淋压力分别为0.05MPa、0.1MPa、0.2MPa和无喷淋情况下木垛火源热释放速率的变化以及火羽流附近几个关键点的温度变化。结果表明,对于热释放速率为0.5MW的木垛火源,压力为0.05MPa和0.1MPa的喷淋液滴无法穿透火羽流到达火源,对热释放速率影响很小;而压力为0.2MPa的喷淋液滴则可穿透火羽流。在火源中心线竖向高度上,存在着喷淋与羽流相互作用的临界面。在临界面以上,温度沿竖向高度降低,喷淋动量大于羽流动量;在临界面以下,温度沿竖向高度升高,羽流动量大于喷淋动量。在火源邻近位置的不同竖向高度上,存在着温度转折点。在转折点以下,温度沿竖向高度几乎不变或变化很小;在转折点以上,温度沿竖向高度升高。

The paper is concerned about a numerical simulation formulated by its authors aiming to disclose the interactive process of the sprinkling water droplets with the fire plume induced by a wood crib fire in a cabin. For the research purpose, we have done an investigation over the effects of the sprinkling spray on the HRR of the fire and the temperature field under different discharge pressures. The results of our investigation have disclosed that the bigger the pressure of the sprinkling water droplets, the greater the penetration capacity would be generated for the droplets, and in turn the quicker the heat releasing rate decreases. Therefore, the sprinkler droplets won＇t be able to penetrate the plume to reach the fire source before the pressure reaches 0. 2 MPa and therefore there would be litde influence on the HRR under the pressure of 0.05 MPa and 0.1 MPa. The reason for this is that there exists a critical transitional point for the vertical temperature distribution at the fire plume axis. Beyond the point, the sprinkler inertial force would be dispersing and the temperature would decrease with the height increase, while, below the point, the fire plume buoyancy would be prevailing with the temperature increased and the height increased. As for the vertical temperature distribution around the fire plume, there also exists a transitional point, Below the point, the temperature would change little in a vertical direction, while, above that point, the temperature would rise with the increase of the height.