Lamprecht Andreas, Schwarz Thomas, Wang Jingtao, Dual Jurg
Department of Mechanical and Process Engineering, Institute for Mechanical Systems, ETH Zurich, Zurich, Switzerland.
J Acoust Soc Am. 2015 Jul;138(1):23-32. doi: 10.1121/1.4922175.
This paper reports the experimental results of the acoustic rotation of spherical micro particles because of two orthogonal standing waves. When the standing waves are excited at equal frequency but with a phase shift between two external voltage signals there is an acoustic streaming around the particles. This streaming is due to a time averaging of the acoustic wave field and produces a nonzero viscous torque on the particles, driving them to rotate. The work investigates the micro-particle rotation due to the viscous torque and predict the particle's steady state rotational velocity. The previous theoretical discussions [Nyborg, J. Acoust. Soc. Am. 85, 329-339 (1958); Lee and Wang, J. Acoust. Soc. Am. 85, 1081-1088 (1989)] of the viscous torque on a non-rotating sphere are expanded to allow free rotations. The analytical calculations provide a deeper understanding of the viscous torque and explain the experimental observations of rotating particles. A macroscopic experimental device is designed to provide the necessary boundary conditions for the viscous torque to rotate spherical particles. The experiments not only show good agreement with the analysis, but also demonstrate that the viscous torque due to acoustic streaming may dominate for the case of near-spherical particle dynamics.
本文报道了由于两个正交驻波导致球形微粒发生声旋转的实验结果。当以相同频率激发驻波，但两个外部电压信号之间存在相位差时，微粒周围会产生声流。这种声流是由于声波场的时间平均效应产生的，会在微粒上产生非零的粘性扭矩，驱动它们旋转。这项工作研究了由粘性扭矩引起的微粒旋转，并预测了微粒的稳态旋转速度。先前关于非旋转球体上粘性扭矩的理论讨论[尼伯格，《美国声学学会杂志》85，329 - 339(1958年)；李和王，《美国声学学会杂志》85，1081 - 1088(1989年)]被扩展到允许自由旋转的情况。解析计算为粘性扭矩提供了更深入的理解，并解释了旋转微粒的实验观测结果。设计了一个宏观实验装置，为粘性扭矩使球形微粒旋转提供必要的边界条件。实验不仅与分析结果吻合良好，还表明对于近球形微粒动力学情况，由声流引起的粘性扭矩可能起主导作用。
