Onset of entrainment in transitional round fountains
Onset of entrainment in transitional round fountains
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DOI：
10.1016/j.ijheatmasstransfer.2008.02.047
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发表时间：
2008-10
影响因子：
5.2
通讯作者：
Wenxian Lin;S. Armfield
中科院分区：
文献类型：
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作者：
Wenxian Lin;S. Armfield
了解具有中间弗劳德数和雷诺数的过渡喷泉的行为以及相关的卷吸和湍流具有根本的意义。本文采用直接数值模拟的方法研究了1 μ Fr ~（80）和200 μ Re ~（800）的轴对称喷泉的瞬态特性。结果表明，当Re ≥ 200时，即使Fr值高达8，在上升流-下降流界面和下降流-环境界面处也几乎没有卷吸现象;然而，当Re>200时，卷吸现象出现在这些界面处，且卷吸程度随Re的增加而增加，这清楚地表明卷吸现象强烈地依赖于Re，而Fr效应的贡献相对较小。DNS的结果还表明，zm，这是最大的喷泉穿透高度，波动，即使当流动达到充分发展，由于在上升流-下降流和下降流-环境界面的卷吸，和平均zm尺度与Fr 32 Re 14为1<Fr 108和100 μ Re 1000。
It is of fundamental interest to understand the behavior of transitional fountains with intermediate Froude and Reynolds numbers, together with the associated entrainment and turbulence. In this work, the transient behavior of axisymmetric fountains with 1⩽Fr⩽8 and 200⩽Re⩽800 is studied by direct numerical simulation. It is found that at Re⩽200, there is little entrainment present at the upflow–downflow interface and at the downflow–ambient interface, even for a value of Fr as high as 8; however, at Re>200, entrainment is present at these interfaces and the extent increases with Re, which clearly demonstrates that entrainment is strongly dependent on Re whereas the contribution from the Fr effect is relatively much smaller. The DNS results also show that zm, which is the maximum fountain penetration height, fluctuates, even when the flow reaches full development, due to the entrainment at the upflow–downflow and the downflow–ambient interfaces, and the averaged zmscales with Fr32Re14for 1<Fr⩽8 and 100⩽Re⩽800.