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A study of the flow-field evolution and mixing in a planar turbulent jet using direct numerical simulation

机译：直接数值模拟研究平面湍流射流的流场演化与混合

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Turbulent plane jets are prototypical free shear flows of practical interest in propulsion. combustion and environmental flows. While considerable experimental research has been performed on planar jets, very few computational studies exist. To the authors' knowledge, this is the first computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation. Jet growth rates as well as the mean velocity, mean scalar and Reynolds stress profiles compare well with experimental data. Coherency spectra, vorticity visualization and autospectra are obtained to identify inferred structures. The development of the initial shear layer instability, as well as the evolution into the jet column mode downstream is captured well. The large- and small-scale anisotropies in the jet are discussed in detail. It is shown that, while the large scales in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly. Near the centreline of the jet, the small scales of turbulence are more isotropic. The mixing process is studied through analysis of the probability density functions of a passive scalar. Immediately after the rollup of vortical structures in the shear layers, the mixing process is dominated by large-scale engulfing of fluid. However, small-scale mixing dominates further downstream in the turbulent core of the self-similar region of the jet and a change from non-marching to marching PDFs is observed. Near the jet edges, the effects of large-scale engulfing of coflow fluid continue to influence the PDFs and non-marching type behaviour is observed. [References: 47]
机译：湍流平面射流是推进中具有实际意义的原型自由剪切流。燃烧和环境流量。尽管已经对平面射流进行了大量的实验研究，但很少有计算研究。据作者所知，这是首次使用直接数值模拟对空间演化的三维平面湍流射流进行的计算研究。射流的生长速度以及平均速度，平均标量和雷诺应力曲线与实验数据相比较。获得相干光谱，涡度可视化和自动光谱来识别推断的结构。很好地捕获了初始剪切层不稳定性的发展以及下游向射流柱模式的演化。详细讨论了射流中的大尺度和小尺度各向异性。结果表明，虽然流场中的大尺度缓慢地调节以适应局部平均速度梯度的变化，但小尺度却迅速地调节。在射流中心线附近，小尺度的湍流更加各向同性。通过分析无源标量的概率密度函数来研究混合过程。在剪切层中涡旋结构卷起后，混合过程立即被大量流体吞噬所支配。但是，小规模混合在射流自相似区域湍流核心的更下游占主导地位，并且观察到了从非前进PDF到前进PDF的变化。在射流边缘附近，同流流体的大规模吞没影响继续影响着PDF，并且观察到非行进型行为。 [参考：47]

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