论文标题
在湍流中的细长旋转游泳者的积累和对齐
Accumulation and alignment of elongated gyrotactic swimmers in turbulence
论文作者
论文摘要
我们研究旋转游泳者在湍流中的动力学，其方向受重力扭矩和局部流体速度梯度的控制。陀螺力强度是通过重力造成的kolmogorov时间尺度与重新定向时间尺度的比例来衡量的，并且该比率很大，这意味着陀螺仪很强。通过直接数值模拟，我们研究了游泳速度和旋转稳定性对空间积累和比对的影响。三维Vorono {\“ı}分析用于研究粒子浓度的空间分布和时间演化。我们通过检查整体优先采样以及簇和voids（分别具有小且大伏罗尼奥{\ \“ \”ı} bolumes的颗粒的子集（分别具有小的粒子）来研究空间分布。与合奏颗粒相比，发现簇和空隙的优先采样更为明显。快速游泳者的聚集持续时间比速度强大且中间的游泳者的持续时间要长得多，但是当陀螺仪较弱时，趋势出现了相反的趋势。此外，我们研究了与拉格朗日拉伸方向的优惠对齐，已知被动的细长杆可以对齐。我们表明，当陀螺仪较弱时，游泳速度降低了拉格朗日的对准，而对于陀螺仪强大的政权，拉格朗日对准会增强。
We study the dynamics of gyrotactic swimmers in turbulence, whose orientation is governed by gravitational torque and local fluid velocity gradient. The gyrotaxis strength is measured by the ratio of the Kolmogorov time scale to the reorientation time scale due to gravity, and a large value of this ratio means the gyrotaxis is strong. By means of direct numerical simulations, we investigate the effects of swimming velocity and gyrotactic stability on spatial accumulation and alignment. Three-dimensional Vorono{\"ı} analysis is used to study the spatial distribution and time evolution of the particle concentration. We study spatial distribution by examing the overall preferential sampling and where clusters and voids (subsets of particles that have small and large Vorono{\"ı} volumes respectively) form. Compared with the ensemble particles, the preferential sampling of clusters and voids is found to be more pronounced. The clustering of fast swimmers lasts much longer than slower swimmers when the gyrotaxis is strong and intermediate, but an opposite trend emerges when the gyrotaxis is weak. In addition, we study the preferential alignment with the Lagrangian stretching direction, with which passive slender rods have been known to align. We show that the Lagrangian alignment is reduced by the swimming velocity when the gyrotaxis is weak, while the Lagrangian alignment is enhanced for the regime in which gyrotaxis is strong.
