论文标题
在树冠流中拉格朗日统计的小规模和大规模间歇性上
On small-scale and large-scale intermittency of Lagrangian statistics in canopy flow
论文作者
论文摘要
冠层流中流体与表面安装的障碍物的相互作用导致强烈的湍流，在中性稳定的大气表面层中主导分散和混合。这项工作着重于树冠流中拉格朗日速度统计的间歇性，这是两种不同形式的观察。第一个小规模间歇性是由非高斯和不是自相似统计的速度增量表达的。该分析表明，与使用多型模型，扩展的自相似性和加速自相关相比，与同质各向同性湍流（HIT）的先前结果相比，一致。这些观察结果表明，冠层流中小规模拉格朗日间歇性的图片与命中相似，因此，它们将普遍拉格朗日间间歇性的概念扩展到某些不均匀和各向异性流动。其次，观察到沿拉格朗日轨迹的能量增量RMS取决于轨迹平均湍流速度的方向。随后的分析表明，在使结构函数的缩放不变的同时，冠层阻力减弱了流动。该观察结果意味着拉格朗日统计中存在大规模间歇性。因此，这项工作提供了冠层流中间歇性拉格朗日速度统计量的第一个经验证据，该冠层流具有两种不同的感觉，并且由于不同的机制而发生。
The interaction of fluids with surface-mounted obstacles in canopy flows leads to strong turbulence that dominates dispersion and mixing in the neutrally stable atmospheric surface layer. This work focuses on intermittency in the Lagrangian velocity statistics in a canopy flow, which is observed in two distinct forms. The first, small scale intermittency, is expressed by non-Gaussian and not self-similar statistics of the velocity increments. The analysis shows an agreement in comparison with previous results from homogeneous isotropic turbulence (HIT) using the multifractal model, extended self-similarity, and acceleration autocorrelations. These observations suggest that the picture of small-scale Lagrangian intermittency in canopy flows is similar to that in HIT, and therefore, they extend the idea of universal Lagrangian intermittency to certain inhomogeneous and anisotropic flows. Second, it is observed that the RMS of energy increments along Lagrangian trajectories depend on the direction of the trajectories' time-averaged turbulent velocity. Subsequent analysis suggests that the flow is attenuated by the canopy drag while leaving the structure function's scaling unchanged. This observation implies the existence of large-scale intermittency in Lagrangian statistics. Thus, this work presents a first empirical evidence of intermittent Lagrangian velocity statistics in a canopy flow that exists in two distinct senses and occurs due to different mechanisms.
