均匀剪切流中惯性颗粒的各向异性聚团
Anisotropic clustering of inertial particles in homogeneous shear flow
摘要：
最近，统计均匀各向同性流的湍流中的惯性粒子的聚类已被彻底分析。从现象学上讲，颗粒配置的空间均匀性被颗粒的斯托克斯弛豫时间决定的一系列涡流的平流破坏，这导致局部浓度和空隙的多尺度分布。关于各向异性流，我们所知甚少。在这里，通过解决直接数值模拟（DNS）的一个统计稳定的颗粒负载均匀剪切流，我们提供的证据表明，平均剪切优先定向颗粒图案。通过在大尺度速度波动上留下各向异性的印记，剪切间接地影响了团簇的几何形状。定量评价是由一个专门设计的工具，粒子对的角分布函数（ADF），它允许解决的各向异性内容的颗粒聚集体的规模的基础上。数据提供的证据表明，根据斯托克斯弛豫时间的颗粒，各向异性聚类可能会发生，即使在规模范围内的载体相速度场已经恢复各向同性。ADF的各向异性分量中的奇异性的强度量化了精细尺度各向异性的水平，其甚至可以达到在粘性尺度分离处找到两个邻近颗粒的概率中的大于30%的方向相关变化的值。
英文摘要：
Recently, clustering of inertial particles in turbulence has been thoroughly analyzed for statistically homogeneous isotropic flows. Phenomenologically, spatial homogeneity of particles configurations is broken by the advection of a range of eddies determined by the Stokes relaxation time of the particles which results in a multi-scale distribution of local concentrations and voids. Much less is known concerning anisotropic flows. Here, by addressing direct numerical simulations (DNS) of a statistically steady particle-laden homogeneous shear flow, we provide evidence that the mean shear preferentially orients particle patterns. By imprinting anisotropy on large scales velocity fluctuations, the shear indirectly affects the geometry of the clusters. Quantitative evaluation is provided by a purposely designed tool, the angular distribution function of particle pairs (ADF), which allows to address the anisotropy content of particles aggregates on a scale by scale basis. The data provide evidence that, depending on the Stokes relaxation time of the particles, anisotropic clustering may occur even in the range of scales where the carrier phase velocity field is already recovering isotropy. The strength of the singularity in the anisotropic component of the ADF quantifies the level of fine scale anisotropy, which may even reach values of more than 30% direction-dependent variation in the probability to find two close-by particles at viscous scale separation.
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