Microbubble streaming in a microfluidic device has been increasingly studied and used in recent years, due to its unique flow pattern that can promote mixing, sort particles and trap particles in microscale flows. However, there have been few numerical studies of this subject. We performed a 3D direct simulation of a cylindrical-shaped micro-bubble, trapped in a pit of a microchannel and sandwiched between two parallel plates, vibrated by pressure oscillation. Our simulation was able to reproduce the experimentally observed relation between the bubble protrusion depth and the vortex pattern: As the bubble protrusion depth increased, new vortices emerged and grew larger. Our investigation of the streamlines near the bubble interface indicates that the number of non-spherical nodes in the bubble interface is closely related to the flow pattern in the liquid phase. It was also validated by our simulation that the flow velocity showed an exponentially decaying trend as the radial distance outward from the vortex center. Our numerical model was also used to investigate the effects of surface tension and channel size on the vortex pattern. Larger surface tension or smaller channel size showed a similar effect as the increased protrusion depth induced more vortices.

中文翻译：

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微流体装置中微气泡流动的直接数值模拟：气泡突出深度对涡流模式的影响

近年来，微流体装置中的微气泡流得到越来越多的研究和使用，因为其独特的流动模式可以促进微流中的粒子混合、分选和捕获粒子。然而，关于这个主题的数值研究很少。我们对圆柱形微气泡进行了 3D 直接模拟，该气泡被困在微通道的坑中并夹在两个平行板之间，通过压力振荡振动。我们的模拟能够重现实验观察到的气泡突出深度与涡流模式之间的关系：随着气泡突出深度的增加，新的涡流出现并变大。我们对气泡界面附近流线的研究表明，气泡界面中非球形节点的数量与液相中的流动模式密切相关。我们的模拟也验证了流速随着从涡流中心向外的径向距离呈指数衰减趋势。我们的数值模型还用于研究表面张力和通道尺寸对涡流图案的影响。较大的表面张力或较小的通道尺寸显示出类似的效果，因为增加的突起深度会引起更多的涡流。我们的数值模型还用于研究表面张力和通道尺寸对涡流图案的影响。较大的表面张力或较小的通道尺寸显示出类似的效果，因为增加的突起深度会引起更多的涡流。我们的数值模型还用于研究表面张力和通道尺寸对涡流图案的影响。较大的表面张力或较小的通道尺寸显示出类似的效果，因为增加的突起深度会引起更多的涡流。