Turbulence induces rotation in the living and the non-living materials in the ocean. The time scale of rotation for a living organism is important in understanding an organism's feeding efficiency, mating, prey capture rate, etc. This time scale is also crucial for understanding the migration of non-living materials such as microplastics. Herein, we investigate the tumbling motion of mesoscale particles that resemble organisms of intermediate size, such as zooplankton that appear in the ocean. Using time-resolved measurements of the orientation of rigid inertial fibers in a turbulence-tank, we analyze the autocorrelation of their tumbling rate. The correlation time (τd) is well-predicted by Kolmogorov inertial-range scaling based on the fiber length (L) when the fiber inertia can be neglected. For inertial fibers, we propose a simple model considering fiber inertia (measured by a tumbling Stokes number) and a viscous torque which accurately predicts both the correlation time and the variance of the tumbling rate. Our measurements and the theoretical model provide a basic understanding of the rotational response of an intermediately sized organism to the surrounding turbulence in its non-active state.

中文翻译：

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湍流中中尺度粒子被动旋转的拉格朗日时间尺度

湍流引起海洋中生物和非生物材料的旋转。生物体旋转的时间尺度对于理解生物体的进食效率、交配、猎物捕获率等很重要。这个时间尺度对于理解微塑料等非生命材料的迁移也很重要。在这里，我们研究了类似于中等大小的生物的中尺度粒子的翻滚运动，例如出现在海洋中的浮游动物。使用湍流罐中刚性惯性纤维方向的时间分辨测量，我们分析了它们的翻滚率的自相关。当光纤惯性可以忽略时，基于光纤长度 (L) 的 Kolmogorov 惯性范围缩放可以很好地预测相关时间 (τd)。对于惯性纤维，我们提出了一个简单的模型，它考虑了纤维惯性（通过翻滚斯托克斯数测量）和粘性扭矩，它可以准确预测相关时间和翻滚速率的方差。我们的测量和理论模型提供了对中等大小的生物体在其非活动状态下对周围湍流的旋转响应的基本理解。