A Lagrangian perspective has yielded many new insights in our quest to reveal the intricacies of turbulent flows. Much of this progress has been possible by following the trajectories of idealised, inertialess objects (tracers) traversing through the flow. Their spins and tumbles provide a glimpse into the underlying local velocity gradients of the turbulent field. While it is known that the spinning and tumbling rates of anisotropic particles are modified in turbulence – compared with those in a random flow field – a quantitative explanation for this has remained elusive. Now, Pujara et al. (J. Fluid Mech., vol. 922, 2021, R6) have made an attempt to predict the split between spinning and tumbling rates by accessing the particle's alignment with the local vorticity. Their analysis of filtered turbulent fields reveals a Lagrangian scale invariance, whereby key quantities relating to the particle's rotational statistics are preserved from the dissipative to the integral scale.

中文翻译：

---

湍流中尺度不变的旋转和翻滚

拉格朗日观点为我们揭示湍流的复杂性提供了许多新见解。通过遵循理想化的无惯性物体（示踪剂）穿过流动的轨迹，大部分进展都是可能的。它们的旋转和翻滚提供了对湍流场潜在局部速度梯度的一瞥。虽然众所周知，各向异性粒子的自旋和翻滚率在湍流中发生了变化——与随机流场中的相比——对此的定量解释仍然难以捉摸。现在，普哈拉等。(J.流体机械。, 卷。922, 2021, R6) 试图通过访问粒子与局部涡度的对齐来预测旋转和翻滚速率之间的分裂。他们对过滤后的湍流场的分析揭示了拉格朗日尺度不变性，即与粒子旋转统计相关的关键量从耗散尺度保留到积分尺度。