Alignment of inertialess spheroidal particles in flow-structure-dominated regions of turbulent channel flow:shape effect  

槽道湍流中无惯性椭球颗粒在结构主导区域的取向行为:形状影响

作　　者：Zhiwen Cui Lihao Zhao 崔智文;赵立豪

机构地区：[1]Applied Mechanics Laboratory,Department of Engineering Mechanics,Tsinghua University,Beijing,100084,China [2]Laboratory of Flexible Electronics Technology,Tsinghua University,Beijing,100084,China

出　　处：《Acta Mechanica Sinica》2024年第8期45-66,共22页力学学报（英文版）

基　　金：supported by the Natural Science Foundation of China(Grant Nos.92252104,92252204,12388101,and 12302285);the China Postdoctoral Science Foundation(Grant No.2022M721849).

摘　　要：The alignment of elongated fibers and thin disks is known to be significantly influenced by the presence of fluid coherent structures in near-wall turbulence(Cui et al.2021).However,this earlier study is confined to the spheroids with infinitely large or small aspect ratio,and the shape effect of finite aspect ratio on the alignment is not considered.The current study investigates the shape-dependent alignment of inertialess spheroids in structure-dominated regions of channel flow.With utilizing an ensemble-averaged approach for identifying the structure-dominated regions,we analyze the eigensystem of the linear term matrix in the Jeffery equation,which is governed by both particle shape and local fluid velocity gradients.In contrast to earlier conventional analysis based on local vorticity and strain rate,our findings demonstrate that the eigensystem of the Jeffery equation offers a convenient,effective,and universal framework for predicting the alignment behavior of inertialess spheroids in turbulent flows.By leveraging the eigensystem of the Jeffery equation,we uncover a diverse effect of fluid coherent structures on spheroid alignment with different particle shapes.Furthermore,we provide explanations for both shape-independent alignments observed in vortical-core regions and shape-dependent alignments around near-wall streamwise vortices.近壁湍流中流动相干结构对纤维和碟状颗粒取向行为的影响显著(Cui et al.,2021).然而,这项早期研究仅限于长细比无限大或无限小的椭球颗粒,而未考虑颗粒有限长细比对取向行为的影响.本研究聚焦于槽道湍流的结构主导区域中,无惯性椭球体的取向与形状之间的关系.在结构主导区域中,本研究对Jeffery方程中线性项矩阵的特征系统进行分析,该线性矩阵由颗粒形状和局部流体速度梯度组成.相较于传统基于颗粒附近的涡量和变形率张量分析方法,本研究利用Jeffery方程的特征系统进行分析为预测无惯性椭球颗粒在湍流中的取向行为提供了一个方便、有效和通用的框架.通过Jeffery方程的特征系统,研究揭示了流动相干结构对具有不同形状的椭球颗粒取向行为的影响规律.此外,在结构主导区域中,本研究对涡核区域观察到与形状无关的取向和近壁流向涡结构周围的形状依赖取向进行了解释.

关 键 词：Non-spherical particle Direct numerical simulation Wall turbulence Particle-laden flow 

分 类 号：O357.5[理学—流体力学]