Wang Ziqi, de Wit Xander M, Toschi Federico
Department of Applied Physics and Science Education, Eindhoven University of Technology, Eindhoven 5600 MB, Netherlands.
Istituto per le Applicazioni del Calcolo "M. Picone", Consiglio Nazionale delle Ricerche, Rome I-00185, Italy.
Proc Natl Acad Sci U S A. 2024 Sep 17;121(38):e2405459121. doi: 10.1073/pnas.2405459121. Epub 2024 Sep 11.
Small bubbles in fluids rise to the surface due to Archimede's force. Remarkably, in turbulent flows this process is severely hindered by the presence of vortex filaments, which act as moving potential wells, dynamically trapping light particles and bubbles. Quantifying the statistical weights and roles of vortex filaments in turbulence is, however, still an outstanding experimental and computational challenge due to their small scale, fast chaotic motion, and transient nature. Here we show that, under the influence of a modulated oscillatory forcing, the collective bubble behavior switches from a dynamically localized to a delocalized state. Additionally, we find that by varying the forcing frequency and amplitude, a remarkable resonant phenomenon between light particles and small-scale vortex filaments emerges, likening particle behavior to a forced damped oscillator. We discuss how these externally actuated bubbles can be used as a type of microscopic probe to investigate the space-time statistical properties of the smallest turbulence scales, allowing to quantitatively measure physical characteristics of vortex filaments. We develop a superposition model that is in excellent agreement with the simulation data of the particle dynamics which reveals the fraction of localized/delocalized particles as well as characteristics of the potential landscape induced by vortices in turbulence. Our approach paves the way for innovative ways to accurately measure turbulent properties and to the possibility to control light particles and bubble motions in turbulence with potential applications to oceanography, medical imaging, drug/gene delivery, chemical reactions, wastewater treatment, and industrial mixing.
流体中的小气泡由于阿基米德力而上升到表面。值得注意的是，在湍流中，这个过程会受到涡旋丝的严重阻碍，涡旋丝就像移动的势阱，动态地捕获轻粒子和气泡。然而，由于涡旋丝的尺度小、运动混沌且具有瞬态性质，量化其在湍流中的统计权重和作用仍然是一个悬而未决的实验和计算难题。在这里，我们表明，在调制振荡力的影响下，气泡的集体行为从动态局域状态转变为非局域状态。此外，我们发现，通过改变力的频率和振幅，轻粒子和小尺度涡旋丝之间会出现显著的共振现象，将粒子行为比作受迫阻尼振荡器。我们讨论了如何将这些外部驱动的气泡用作一种微观探针，以研究最小湍流尺度的时空统计特性，从而能够定量测量涡旋丝的物理特性。我们开发了一个叠加模型，该模型与粒子动力学的模拟数据非常吻合，揭示了局域化/非局域化粒子的比例以及湍流中涡旋引起的势场特征。我们的方法为准确测量湍流特性的创新方法以及控制湍流中轻粒子和气泡运动的可能性铺平了道路，这在海洋学、医学成像、药物/基因递送、化学反应、废水处理和工业混合等领域具有潜在应用。
