Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet
Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet
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湍流射流中高施密特数被动标量的微分扩散
DOI：
10.1017/s0022112008003224
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发表时间：
2008
影响因子：
3.7
通讯作者：
S. Gaskin
中科院分区：
文献类型：
--
作者：
T. Lavertu;L. Mydlarski;S. Gaskin
实验研究了湍流射流中高施密特数被动标量的分离演化或微分扩散。所考虑的两种标量是荧光素二钠（Sc = 2000）和磺酰罗丹明101（Sc = 5000）。研究的目的是双重的：以确定（i）的Bolds-number依赖性，和（ii）的径向分布的差异扩散效应的自相似区域的射流。在五个雷诺数下，在喷嘴出口下游50个射流直径处获得了准时的激光诱导荧光（LIF）测量结果（Re ω uod/ν = 900、2100、4300、6700和10600，其中u 0是射流出口速度，d是射流直径，和ν是运动粘度）和从射流横截面的中心线延伸到边缘的径向位置（0 ≤ r/d ≤ 7.5）。使用归一化浓度差Z的统计量来量化微分扩散。后者被发现随着雷诺数的增加而缓慢衰减，Z标度的均方根为Zrms Z2 Re−0.2）。无论雷诺数，微分扩散效应被发现增加远离中心线。差异扩散效应随径向位置的增加，沿着随着雷诺数的降低而增加，支持射流与环境流体之间界面处差异扩散增加的假设。还研究了Z的功率谱密度。这些光谱随着波数的增加而减少-这是由于湍流射流中标量波动衰减的结果。此外，这些光谱表明，显着的微分扩散效应持续在尺度大于Kolmogorov尺度，即使是适度高的雷诺数。
The separate evolution, or differential diffusion, of high-Schmidt-number passive scalars in a turbulent jet is studied experimentally. The two scalars under consideration are disodium fluorescein (Sc ≡ ν/D = 2000) and sulforhodamine 101 (Sc = 5000). The objectives of the research are twofold: to determine (i) the Reynolds-number-dependence, and (ii) the radial distribution of differential diffusion effects in the self-similar region of the jet. Punctual laser-induced fluorescence (LIF) measurements were obtained 50 jet diameters downstream of the nozzle exit for five Reynolds numbers (Re ≡ uod/ν = 900, 2100, 4300, 6700 and 10600, where u0 is the jet exit velocity, d is the jet diameter, and ν is the kinematic viscosity) and for radial positions extending from the centreline to the edges of the jet cross-section (0 ≤ r/d ≤ 7.5). Statistics of the normalized concentration difference, Z, were used to quantify the differential diffusion. The latter were found to decay slowly with increasing Reynolds number, with the root mean square of Z scaling as Zrms ≡ 〈Z2〉1/2 ∝ Re−0.1, (or alternatively 〈Z2〉 ∝ Re−0.2). Regardless of Reynolds number, differential diffusion effects were found to increase away from the centreline. The increase in differential diffusion effects with radial position, along with their increase with decreasing Reynolds number, support the hypothesis of increased differential diffusion at interfaces between the jet and ambient fluids. Power spectral densities of Z were also studied. These spectra decreased with increasing wavenumber – an observation attributed to the decay of the scalar fluctuations in a turbulent jet. Furthermore, these spectra showed that significant differential diffusion effects persist at scales larger than the Kolmogorov scale, even for moderately high Reynolds numbers.