The behaviour of the scalar gradient across the turbulent/non-turbulent interface in jets
The behaviour of the scalar gradient across the turbulent/non-turbulent interface in jets
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DOI：
10.1063/1.4997951
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发表时间：
2017-08
影响因子：
4.6
通讯作者：
Tiago S. Silva;C. Silva
中科院分区：
文献类型：
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作者：
Tiago S. Silva;C. Silva
通过对雷诺数为14 2≤Reλ≤2 46，施密特数为0.0 7≤S c≤7.0 7的平面湍流射流的直接数值模拟，分析了湍流/非湍流界面附近被动标量场的动力学特性。在射流外缘形成标量梯度湍流/非湍流界面(SG-TNTI)，在较低施密特数(SC=0.07和0.7)的情况下，这与涡度湍流/非湍流界面(VO-TNTI)不一致。具体地说，对于SC=0.07和0.7，标量梯度极大值，因此大部分混合发生在无旋区，距离VO-TNTI的开始处10到30 Kolmogorov微尺度距离。对于中等施密特数情形，SG-TNTI表现为无旋扩散层，其中标量梯度扩散占主导地位，而产生可以忽略不计，其次是无旋应变亚层，其中标量梯度产生占主导。对于Sc=7.0，SG-TNTI由一个与VO-TNTI粘性超层紧密匹配的v对流超层和一个惯性对流亚层组成，其中标量梯度产物占主导地位，后者比VO-TNTI的湍流亚层小得多。简要讨论了各(子)层的标度律和平均厚度。本文系统地研究了施密特数对标量梯度演化和SG-TNTI特性的影响。
The dynamics of a passive scalar field near a turbulent/non-turbulent interface is analysed through direct numerical simulations of turbulent planar jets, with Reynolds numbers ranging from 142 ≤ R e λ ≤ 246 , and Schmidt numbers from 0.07 ≤ S c ≤ 7.0 . A scalar-gradient turbulent/non-turbulent interface (SG-TNTI) forms at the outer edge of the jet, which does not coincide with the vorticity turbulent/non-turbulent interface (VO-TNTI) for the lower Schmidt number cases (Sc = 0.07 and 0.7). Specifically, for Sc = 0.07 and 0.7, the scalar gradient maxima, and thus the bulk of the mixing takes place in the irrotational region, between 10 and 30 Kolmogorov micro-scale distances from the start of the VO-TNTI. For these moderate Schmidt number cases, the SG-TNTI exhibits an irrotational-diffusive superlayer, where the scalar gradient diffusion dominates, while the production is negligible, followed by an irrotational-straining sublayer where the scalar gradient production dominates. In contrast for Sc = 7.0, the SG-TNTI consists of a v iscous-con v ective superlayer that closely matches the viscous superlayer from the VO-TNTI and an inertial-convective sublayer, where scalar gradient production dominates, which is much smaller than the turbulent sublayer of the VO-TNTI. The scaling laws and mean thicknesses of each one of these (sub)layers are briefly discussed. This work presents a systematic study of the effects of the Schmidt number on the scalar gradient evolution and of the SG-TNTI characteristics.