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arXiv 2401.12693physics.flu-dyn
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接触角滞后对黏弹性两相系统中液滴的影响

The effect of contact angle hysteresis on a droplet in a viscoelastic two-phase system

Kazem Bazesefidpar, Outi Tammisola

AI总结:

本研究模拟低雷诺数泊肃叶流中壁面液滴,揭示液滴或周围介质黏弹性、Deborah 数、毛细数及 Giesekus 参数对接触线运动和变形的非单调影响。

摘要:

我们研究了低雷诺数下泊肃叶流中附着在壁面上的二维(2D)液滴的动力学行为,该系统中要么液滴是黏弹性的(V/N),要么周围介质是黏弹性的(N/V)。结果表明,由于聚合物分子的存在,黏弹性液滴随时间的变形发生了改变。在第一阶段,黏弹性液滴加速且变形更快,而在第二阶段,牛顿对应物加速,其变形超过黏弹性液滴。随着 Deborah 数 $De$ 的增加,黏弹性液滴的变形在第二阶段显著延迟。在 V/N 情形下,对于较小的 $De$,后退侧的黏性弯曲增强,但随着 $De$ 进一步增加而减弱,这种非单调行为导致在小 $De$ 时后退接触线速度增加,而在大 $De$ 时减小。在前进侧,当 $Ca<0.25$ 时黏性弯曲单调减小,因此前进接触线速度随 $De$ 增加而减小;然而,在前进侧 $Ca=0.25$ 时,黏性弯曲呈现非单调行为。后退侧的非单调行为归因于后退接触线附近向外拉应力的出现以及在较高 $De$ 下应变硬化的开始,而前进侧黏性弯曲的减小仅仅是由于前进侧占主导的拉伸流导致应变硬化的结果。最后,在 N/V 系统中,介质的黏弹性抑制了液滴在后退侧和前进侧的变形,并且这种效应随着 De 的增加而更加明显;增加 Giesekus 迁移率参数会显著增强前进侧黏性弯曲的减弱效应。

英文摘要:

We investigate the dynamic behaviour of a two-dimensional (2D) droplet adhering to a wall in Poiseuille flow at low Reynolds numbers, in a system where either the droplet is viscoelastic (V/N) or the surrounding medium (N/V). The results reveal that the deformation of the viscoelastic drop over time is changed due to the presence of polymeric molecules. In the first stage, the viscoelastic droplet speeds up and deforms faster, while in the second stage, the Newtonian counterpart accelerates and its deformation outpaces the viscoelastic droplet. The deformation of viscoelastic drop is retarded significantly in the second stage with increasing Deborah number $De$. In the V/N case, the viscous bending is enhanced on the receding side for small $De$, but it is weakened by further increase in $De$, and this non-monotonic behavior brings about an increase in the receding contact line velocity at small $De$ and a decrease at large $De$. On the advancing side, the viscous bending is decreased monotonically for $Ca<0.25$, and hence the advancing contact line velocity is decreased with increasing $De$; however, the viscous bending presents a non-monotonic behavior for $Ca=0.25$ at the advancing side. The non-monotonic behavior on the receding side is attributed to the emergence of outward pulling stresses in the vicinity of the receding contact line and the inception of strain-hardening at higher $De$, while the reduction in the viscous bending at the advancing side is the result of just strain-hardening due to the presence of dominant extensional flow on the advancing side. Finally, in the N/V system, the viscoelasticity of the medium suppresses the droplet deformation on both receding and advancing sides, and this effect is more pronounced with increasing De; the weakening effect of viscous bending is enhanced significantly at the advancing side by increasing the Giesekus mobility parameter.

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