Martin James E, Solis Kyle J
Sandia National Laboratories, Albuquerque, New Mexico, USA.
Soft Matter. 2015 Jan 14;11(2):241-54. doi: 10.1039/c4sm01936a.
Noncontact methods of generating strong fluid vorticity are important to problems involving heat and mass transfer, fluid mixing, active wetting, and droplet transport. Furthermore, because zero or even negative shear viscosities can be induced, vorticity can greatly extend the control range of the smart fluids used in magnetorheological devices. In recent work we have shown that a particular class of ac/ac/dc triaxial fields (symmetry-breaking rational fields) can create strong vorticity in magnetic particle suspensions and have presented a theory of the vorticity that is based on the symmetry of the 2-d Lissajous trajectories of the field and its converse. In this paper we demonstrate that there are three countably infinite sets of fully alternating ac/ac/ac triaxial fields whose frequencies form rational triads that have the symmetry required to drive fluid vorticity. The symmetry of the 3-d Lissajous trajectories of the field and its converse can be derived and from this the direction of the vorticity axis can be predicted, as can the dependence of the sign of the vorticity on the phase relations between the three field components. Experimental results are presented that validate the symmetry theory. These discoveries significantly broaden the class of triaxial fields that can be exploited to produce strong noncontact flow.
产生强流体涡度的非接触方法对于涉及传热传质、流体混合、主动润湿和液滴传输的问题至关重要。此外，由于可以诱导出零甚至负的剪切粘度，涡度可以极大地扩展磁流变装置中使用的智能流体的控制范围。在最近的工作中，我们已经表明，一类特殊的交流/交流/直流三轴场（破缺对称有理场）可以在磁性颗粒悬浮液中产生强涡度，并提出了一种基于场的二维李萨如轨迹及其逆轨迹对称性的涡度理论。在本文中，我们证明存在三组可数无穷的完全交替交流/交流/交流三轴场，其频率形成有理三元组，具有驱动流体涡度所需的对称性。可以推导出场的三维李萨如轨迹及其逆轨迹的对称性，并由此预测涡度轴的方向，以及涡度符号对三个场分量之间相位关系的依赖性。给出了验证对称性理论的实验结果。这些发现显著拓宽了可用于产生强非接触流的三轴场的类别。
