Oscillations of a cantilevered micro beam driven by a viscoelastic flow instability
Oscillations of a cantilevered micro beam driven by a viscoelastic flow instability
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DOI：
10.1039/c9sm01794a
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发表时间：
2020-02-07
期刊：
影响因子：
3.4
通讯作者：
Rothstein, Jonathan P.
中科院分区：
文献类型：
--
作者：
Dey, Anita A.;Modarres-Sadeghi, Yahya;Rothstein, Jonathan P.
柔性结构与粘弹性流的相互作用可以产生非常丰富的动力学。在本文中，我们给出了粘弹性聚合物溶液与悬臂梁在受限微流体几何结构中相互作用的结果。对变长度、变柔度的悬臂梁进行了研究。随着流量和Weissenberg数的增加，流动从纵向对称流过渡到光束上游稳定的分离涡，再到随时间变化的不稳定涡脱落。梁上游不稳定涡的脱落对悬臂梁施加了随时间变化的阻力，导致了流致的梁振荡。柔性梁的振动可分为两种不同的区域：一种是光束上游有明显的单涡脱落，导致振动频率随Weissenberg数单调增加的正弦光束振荡模式；另一种是以三维粘弹性不稳定性为特征的高Weissenberg数区域，振荡频率持平。文中详细介绍了悬臂梁的临界流动转变开始、旋涡脱落的机理以及悬臂梁响应的动力学特性。
The interaction of flexible structures with viscoelastic flows can result in very rich dynamics. In this paper, we present the results of the interactions between the flow of a viscoelastic polymer solution and a cantilevered beam in a confined microfluidic geometry. Cantilevered beams with varying length and flexibility were studied. With increasing flow rate and Weissenberg number, the flow transitioned from a fore-aft symmetric flow to a stable detached vortex upstream of the beam, to a time-dependent unstable vortex shedding. The shedding of the unstable vortex upstream of the beam imposed a time-dependent drag force on the cantilevered beam resulting in flow-induced beam oscillations. The oscillations of the flexible beam were classified into two distinct regimes: a regime with a clear single vortex shedding from upstream of the beam resulting in a sinusoidal beam oscillation pattern with the frequency of oscillation increasing monotonically with Weissenberg number, and a regime at high Weissenberg numbers characterized by 3D viscoelastic instabilities where the frequency of oscillations plateaued. The critical onset of the flow transitions, the mechanism of vortex shedding and the dynamics of the cantilevered beam response are presented in detail here as a function of beam flexibility and flow viscoelasticity.