Direct numerical simulation of passive scalar mixing in spatially evolving turbulent round jets
Direct numerical simulation of passive scalar mixing in spatially evolving turbulent round jets
复制标题
空间演化湍流圆形射流中被动标量混合的直接数值模拟
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
K. Mahesh
中科院分区：
文献类型：
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作者：
P. Babu;K. Mahesh
在雷诺数为2400，施密特数为1的条件下，对空间演化湍流射流中的标量输运进行了直接数值模拟。计算域延伸到射流出口平面的上游，以允许出口平面附近的夹带。平均速度、平均标量浓度以及速度和标量的波动与实验数据进行了很好的比较。研究了速度和被动标量的瞬时径向分布。速度和标量配置文件被证明是定性相似，并交替之间的“礼帽”和“三角形”的形状。的配置文件被发现是由夹带从自由流到射流，这种行为产生一个高斯平均。研究了扩散在标量输运中的作用及其与混合跃迁的关系。分析了被动标量输运方程中的瞬时对流项和扩散项，确定了扩散主导区域。扩散占主导地位的区域出现在非常薄的区域更接近射流中心。然而，扩散是很重要的相当厚，“刷状”区域附近的射流边缘。射流边缘附近的较高停留时间被认为是造成这种行为的原因。据推测，这些刷状区域决定了雷诺数的标量波动的整体效果。这些外部区域的宽度预计将随着雷诺数的增加而减小，并且假设一旦这些外部区域与射流直径相比变薄，标量波动将经历混合过渡。
Direct numerical simulation of passive scalar transport in a spatially evolving turbulent jet is performed at Reynolds number of 2400 and Schmidt number of unity. The computational domain extends upstream of the jet exit plane to allow for entrainment near the exit plane. Good comparison with experimental data is obtained for the mean velocity, mean scalar concentration, and fluctuations of velocity and scalar. The instantaneous radial profiles of velocity and passive scalar are examined. The velocity and scalar profiles are shown to be qualitatively similar, and alternate between ‘top–hat’ and ‘triangle’ shapes. The profiles are found to be determined by entrainment from the free–stream into the jet and this behavior yields a Gaussian mean. The role of diffusion in scalar transport is studied for its relevance to mixing transition. The instantaneous convective and diffusive terms in the passive scalar transport equation are analyzed, and diffusion–dominated regions are identified. Diffusion–dominated regions occur in very thin regions closer to the jet center. However, diffusion is important over fairly thick, ‘brush–like’ regions near the jet edge. Higher residence times near the jet edge are thought responsible for this behavior. It is speculated that these brush–like regions determine the overall effect of Reynolds number on the scalar fluctuations. The width of these outer regions is expected to decrease with increase in Reynolds number, and the scalar fluctuations are hypothesized to undergo mixing transition once these outer regions are thin compared to the jet diameter.