Effect of the eigenvalues of the velocity gradient tensor on particle collisions
Effect of the eigenvalues of the velocity gradient tensor on particle collisions
复制标题
速度梯度张量特征值对粒子碰撞的影响
DOI：
10.1017/jfm.2016.70
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发表时间：
2016
影响因子：
3.7
通讯作者：
H. Jonker
中科院分区：
文献类型：
--
作者：
V. Perrin;H. Jonker
本文利用局部速度梯度张量的特征值，将不可压湍流中的局部流动结构划分为不同类型的鞍结和涡，并研究了它们对重粒子局部碰撞核的影响。直接数值模拟（DNS）的结果表明，大多数碰撞发生在收敛区域与真实的和负的特征值。这些区域不仅与更强的优先粒子聚集相关联，而且与相对更高的碰撞核相关联。为了更好地理解DNS结果，开发了一个概念框架来计算单个流结构的碰撞核。收敛区域，其中三个特征值中的两个是负的，只要不超过临界旋转量，就具有非常高的碰撞核。发散区域的三个本征值中有两个是正的，具有非常低的碰撞核，其由第三本征值和负本征值控制。这个模型是不适合的粒子与斯托克斯数$St\gg 1$，粒子碰撞焦散的贡献是占主导地位的。
This study uses the eigenvalues of the local velocity gradient tensor to categorize the local flow structures in incompressible turbulent flows into different types of saddle nodes and vortices and investigates their effect on the local collision kernel of heavy particles. Direct numerical simulation (DNS) results show that most of the collisions occur in converging regions with real and negative eigenvalues. Those regions are associated not only with a stronger preferential clustering of particles, but also with a relatively higher collision kernel. To better understand the DNS results, a conceptual framework is developed to compute the collision kernel of individual flow structures. Converging regions, where two out of three eigenvalues are negative, posses a very high collision kernel, as long as a critical amount of rotation is not exceeded. Diverging regions, where two out of three eigenvalues are positive, have a very low collision kernel, which is governed by the third and negative eigenvalue. This model is not suited for particles with Stokes number $St\gg 1$ , where the contribution of particle collisions from caustics is dominant.