Turbulence, entrainment and low-order description of a transitional variable-density jet
Turbulence, entrainment and low-order description of a transitional variable-density jet
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过渡变密度射流的湍流、夹带和低阶描述
DOI：
10.1017/jfm.2017.822
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发表时间：
2018
影响因子：
3.7
通讯作者：
Solovitz, S. A.
中科院分区：
文献类型：
--
作者：
Viggiano, B.;Dib, T.;Ali, N.;Mastin, L. G.;Cal, R. B.;Solovitz, S. A.
地球物理流发生在很大的尺度范围内，雷诺数和理查森数变化几个数量级。在这项研究中，考虑到与某些地球物理现象相关的条件，不同密度的射流被垂直喷射到一个大的周围区域。使用粒子图像测速技术，测量了排入空气中的三种不同气体（特别是氦气、空气和氩气）的速度场。测量集中于射流核心和夹带环境。实验考虑了相对较低的雷诺数，大约为 1500 到 10000，理查森数的大小接近 0.001。其中包括各种流动响应，特别是近层流射流、湍流射流和介于两者之间的过渡射流。研究了几个特征，包括射流发展、局部夹带比、湍流雷诺应力和涡流强度。与完全湍流射流相比，过渡射流显示出高出 50% 的局部夹带和更显着的湍流波动。对于这种情况，涡流是非轴对称的并且大于出口半径。对于湍流射流，涡流最初较小且轴对称，同时随着剪切层增长。在较低的湍流雷诺数下，湍流应力比较高的湍流雷诺数高 50% 以上。无论哪种情况，低密度喷流的发展速度都比同类非浮力喷流要快。还利用象限分析和适当的正交分解来深入了解射流的夹带，以及评估相对于本征模态数量的能量分布。雷诺剪应力在 Q1 和 Q3 中占主导地位，其余两个象限的贡献可以忽略不计。两种分析技术都表明下游应力的发展取决于雷诺数，而应力的翼展位置取决于理查森数。
Geophysical flows occur over a large range of scales, with Reynolds numbers and Richardson numbers varying over several orders of magnitude. For this study, jets of different densities were ejected vertically into a large ambient region, considering conditions relevant to some geophysical phenomena. Using particle image velocimetry, the velocity fields were measured for three different gases exhausting into air – specifically helium, air and argon. Measurements focused on both the jet core and the entrained ambient. Experiments considered relatively low Reynolds numbers from approximately 1500 to 10 000 with Richardson numbers near 0.001 in magnitude. These included a variety of flow responses, notably a nearly laminar jet, turbulent jets and a transitioning jet in between. Several features were studied, including the jet development, the local entrainment ratio, the turbulent Reynolds stresses and the eddy strength. Compared to a fully turbulent jet, the transitioning jet showed up to 50 % higher local entrainment and more significant turbulent fluctuations. For this condition, the eddies were non-axisymmetric and larger than the exit radius. For turbulent jets, the eddies were initially smaller and axisymmetric while growing with the shear layer. At lower turbulent Reynolds number, the turbulent stresses were more than 50 % higher than at higher turbulent Reynolds number. In either case, the low-density jet developed faster than a comparable non-buoyant jet. Quadrant analysis and proper orthogonal decomposition were also utilized for insight into the entrainment of the jet, as well as to assess the energy distribution with respect to the number of eigenmodes. Reynolds shear stresses were dominant in Q1 and Q3 and exhibited negligible contributions from the remaining two quadrants. Both analysis techniques showed that the development of stresses downstream was dependent on the Reynolds number while the spanwise location of the stresses depended on the Richardson number.
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影响因子：
3.7
作者：
RAUPACH, MR
通讯作者：
RAUPACH, MR
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影响因子：
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影响因子：
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1993
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DOI：
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发表时间：
1993
期刊：
影响因子：
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