Tuning a magnetic field to generate spinning ferrofluid droplets with controllable speed via nonlinear periodic interfacial waves
Tuning a magnetic field to generate spinning ferrofluid droplets with controllable speed via nonlinear periodic interfacial waves
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通过非线性周期性界面波调节磁场以产生速度可控的旋转铁磁流体液滴
DOI：
10.1103/physreve.103.013103
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发表时间：
2021
影响因子：
2.4
通讯作者：
Christov, Ivan C.
中科院分区：
文献类型：
--
作者：
Yu, Zongxin;Christov, Ivan C.
Hele-Shaw构型的二维自由表面流动是探索非线性物理的一片沃土。自从Saffman和Taylor对流体-流体界面的线性不稳定性的研究以来，人们已经花费了大量的精力来确定线性增长率的物理和强迫。然而，线性稳定并不总是意味着非线性稳定。我们演示了如何组合的径向和方位角的外部磁场可以操纵的线性不稳定的铁磁流体液滴在Hele-Shaw配置的界面形状。我们表明，弱非线性理论可以用来调整初始不稳定的增长。然后，非线性逮捕的不稳定性，并导致永久变形的液滴形状。具体来说，我们表明，变形液滴可以设置成运动与可预测的旋转速度，演示非线性行波的流体-流体界面。最线性不稳定的波数和施加的外部磁场的组合强度决定了行波形状，该形状可以是不对称的。
Two-dimensional free surface flows in Hele-Shaw configurations are a fertile ground for exploring nonlinear physics. Since Saffman and Taylor's work on linear instability of fluid-fluid interfaces, significant effort has been expended to determining the physics and forcing that set the linear growth rate. However, linear stability does not always imply nonlinear stability. We demonstrate how the combination of a radial and an azimuthal external magnetic field can manipulate the interfacial shape of a linearly unstable ferrofluid droplet in a Hele-Shaw configuration. We show that weakly nonlinear theory can be used to tune the initial unstable growth. Then, nonlinearity arrests the instability and leads to a permanent deformed droplet shape. Specifically, we show that the deformed droplet can be set into motion with a predictable rotation speed, demonstrating nonlinear traveling waves on the fluid-fluid interface. The most linearly unstable wave number and the combined strength of the applied external magnetic fields determine the traveling wave shape, which can be asymmetric.