Dynamic Large-Eddy Simulation of Droplet Effects on a Reacting Plume in Countercurrent Configuration
Dynamic Large-Eddy Simulation of Droplet Effects on a Reacting Plume in Countercurrent Configuration
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DOI：
10.1080/00102202.2010.534517
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发表时间：
2011-02
影响因子：
1.9
通讯作者：
J. Xia;K. Luo;H. Zhao
中科院分区：
文献类型：
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作者：
J. Xia;K. Luo;H. Zhao
采用大涡模拟（LES）和动态亚网格流动模型研究了蒸发液滴对反应羽流的影响。逆流配置用于模拟理想的小规模水基灭火系统，其中液滴向下排放到上升的浮力反应羽流中。通过改变初始斯托克斯数（St 0）或无量纲液滴尺寸、喷嘴体积流量或等效质量负载比（MLR 0）以及初始液滴速度（），独立进行了参数研究。两相之间的相互作用进行了研究，在瞬时和统计手段。液滴对反应羽流的热效应和动力学效应使用气相的过滤（减少）的内能和过滤的动能的传输方程进行了仔细检查。通过将输运方程中的液滴源项重新排列成物理上有意义的项，从而清楚地表示由于液滴的各种贡献，获得了关于液滴效应的新见解。具体地，发现只有相之间的热交换倾向于降低气体温度。所有其他与液滴相关的项，包括相间阻力和蒸发贡献，都是内能的源项，因此倾向于使羽流升温。从网格尺度动能的预算分析，它被发现，液滴的影响所产生的相间阻力和蒸发倾向于减少网格尺度动能，除了在靠近喷嘴的区域。
The effects of evaporating droplets on a reacting plume have been investigated using large-eddy simulation (LES) with dynamic subgrid flow models. A countercurrent configuration, in which droplets are discharged downward toward a rising buoyant reacting plume, is used to mimic an idealized small-scale, water-based fire suppression system. Parametric studies have been conducted by varying the initial Stokes number (St 0) or nondimensional droplet size, volumetric flow rate of the spray nozzle or equivalent mass loading ratio (MLR 0), and initial droplet speed ( ), independently. The interactions between the two phases are studied in both instantaneous and statistical means. The thermal and dynamic effects of droplets on the reacting plume are scrutinized using the transport equations for the filtered (reduced) internal energy and filtered kinetic energy of the gas phase. New insights on the droplet effects have been gained by rearranging the droplet source terms in the transport equations into physically meaningful terms which clearly represent various contributions due to droplets. Specifically, it was found that only the heat exchange between the phases tends to reduce the gas temperature. All the other droplet-related terms, including the interphase drag and evaporation contributions, are source terms to the internal energy and thus tend to warm up the plume. From the budget analysis of the grid-scale kinetic energy, it was found that the droplet effects arising from both the interphase drag and evaporation tend to decrease the grid-scale kinetic energy, except in regions close to the spray nozzle.