Using helicity to investigate scalar transport in wall turbulence
Using helicity to investigate scalar transport in wall turbulence
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DOI：
10.1103/physrevfluids.5.062601
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发表时间：
2020-06-23
影响因子：
2.7
通讯作者：
Papavassiliou, D., V
中科院分区：
文献类型：
--
作者：
Nguyen, Q.;Papavassiliou, D., V
螺旋度，定义为速度和涡度矢量的内积，即使对于层流也难以测量。湍流的理论结果表明，高螺旋度的流动结构与低耗散的动能，使他们的候选人相干结构，可以持续更长的时间比别人在流场。由于湍流中的标量输运被三维相干运动增强，螺旋度的研究可以揭示比其他结构对标量输运贡献更大的流动结构。直接数值模拟的湍流通道流在Re τ = 300结合拉格朗日跟踪的流体粒子和被动标量标记为施密特数0.7和200在这里使用。计算沿这些标记和流体粒子的轨迹的局部螺旋度沿着。不同水平的螺旋度被发现涉及到的概率，这些标记将保持在一个连贯的区域内。拉格朗日螺旋度分布也被提出，表明标量运输标记的速度和涡度矢量之间的对齐的变化。
Helicity, defined as the inner product of the velocity and the vorticity vector, is elusive to measure even for laminar flows. Theoretical results for turbulence have shown that flow structures of high helicity are associated with low dissipation of kinetic energy, making them candidates for coherent structures that can persist longer than others in the flow field. As scalar transport in turbulence is enhanced by three-dimensional coherent motions, study of helicity could reveal flow structures that contribute more than others to scalar transport. Direct numerical simulations of turbulent channel flow at Re-tau = 300 in conjunction with Lagrangian tracking of fluid particles and passive scalar markers for Schmidt numbers 0.7 and 200 are used here. Local helicity along the trajectories of these markers and the fluid particles is calculated. Different levels of helicity are found to relate to the probability that these markers will remain inside a coherent region. The Lagrangian helicity distribution is also presented, indicating a change of the alignment between velocity and vorticity vectors for scalar transport markers.