水-气界面热珠径向热毛细流的方位不稳定性
Azimuthal instability of the radial thermocapillary flow around a hot bead trapped at the water-air interface
摘要：
研究了激光加热微珠在水-气界面局部润湿条件下驱动的径向热毛细流动。特别注意的是周围的热球的对流模式的演变，因为后者是越来越热。在低激光功率P下，流动形态几乎是轴对称的。增加P导致对称性破缺，并出现反向旋转的涡对。在界面处的边界条件，接近无滑移在低P政权，转向约无应力之间的涡对在高P政权。这些观察结果有力地支持了这样的观点，即表面活性杂质不可避免地吸附在水面上，在那里它们形成弹性层。涡对的出现是流体动力学不稳定性在离心力强迫流动的层响应的签名。有趣的是，我们的研究为设计能够通过在液体界面产生涡旋对实现高速自推进的活性胶体铺平了道路。
英文摘要：
We investigate the radial thermocapillary flow driven by a laser-heated microbead in partial wetting at the water-air interface. Particular attention is paid to the evolution of the convective flow patterns surrounding the hot sphere as the latter is increasingly heated. The flow morphology is nearly axisymmetric at low laser power P. Increasing P leads to symmetry breaking with the onset of counter-rotating vortex pairs. The boundary condition at the interface, close to no-slip in the low-P regime, turns about stress-free between the vortex pairs in the high-P regime. These observations strongly support the view that surface-active impurities are inevitably adsorbed on the water surface where they form an elastic layer. The onset of vortex pairs is the signature of a hydrodynamic instability in the layer response to the centrifugal forced flow. Interestingly, our study paves the way for the design of active colloids able to achieve high-speed self-propulsion via vortex pair generation at a liquid interface.
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