破裂气泡产生的黏弹性 Worthington 射流与液滴
Viscoelastic Worthington jets & droplets produced by bursting bubbles
AI总结：
本文通过直接数值模拟揭示黏弹性流体中气泡破裂后的射流与液滴形成规律，依据 $Ec$、$De$ 和 $Oh_s$ 划分三种流动状态。
摘要：
在受污染液体的自由表面，气泡破裂以及随后开口空腔的塌陷会产生气溶胶液滴，从而促进病原体传播。液膜破裂后，毛细波在空腔底部聚焦，可能形成快速的 Worthington 射流，并负责将液滴从源处抛射出去。尽管这一过程在牛顿流体中已得到广泛研究，但非牛顿流变学对其的影响仍知之甚少。本文采用直接数值模拟研究黏弹性介质（如聚合液体）中的气泡空腔塌陷。我们发现，射流和液滴的形成由两个无量纲参数决定：弹毛数 $Ec$（弹性模量与 Laplace 压力之比）和 Deborah 数 $De$（松弛时间与惯性—毛细时间尺度之比）。结果表明，当 $Ec$ 和 $De$ 较低时，黏弹性液体表现出类似牛顿流体的行为，其动力学由溶剂 Ohnesorge 数 $Oh_s$（黏—毛细时间尺度与惯性—毛细时间尺度之比）控制。相反，当 $Ec$ 和 $De$ 较大时，增强的弹性应力会完全抑制射流形成。在某些 $Ec$ 和 $De$ 处于中间值的情况下，与牛顿流体相比会产生更小的液滴，从而可能增强气溶胶扩散。通过绘制由 $Ec$、$De$ 和 $Oh_s$ 张成的相空间，我们揭示了三种不同的流动状态：（i）形成液滴的射流，（ii）不形成液滴的射流，以及（iii）无射流形成。我们的结果阐明了聚合液体中气溶胶抑制与细雾形成背后的机制，并对病原体传播以及涉及黏弹性流体的工业过程具有启示意义。
英文摘要：
Bubble bursting and subsequent collapse of the open cavity at free surfaces of contaminated liquids can generate aerosol droplets, facilitating pathogen transport. After film rupture, capillary waves focus at the cavity base, potentially generating fast Worthington jets that are responsible for ejecting the droplets away from the source. While extensively studied for Newtonian fluids, the influence of non-Newtonian rheology on this process remains poorly understood. Here, we employ direct numerical simulations to investigate the bubble cavity collapse in viscoelastic media, such as polymeric liquids. We find that the jet and drop formation are dictated by two dimensionless parameters: the elastocapillary number $Ec$ (the ratio of the elastic modulus and the Laplace pressure) and the Deborah number $De$ (the ratio of the relaxation time and the inertio-capillary timescale). We show that for low values of $Ec$ and $De$, the viscoelastic liquid adopts a Newtonian-like behavior, where the dynamics are governed by the solvent Ohnesorge number $Oh_s$ (the ratio of visco-capillary and inertio-capillary timescales). In contrast, for large values $Ec$ and $De$, the enhanced elastic stresses completely suppress the formation of the jet. For some cases with intermediate values of $Ec$ and $De$, smaller droplets are produced compared to Newtonian fluids, potentially enhancing aerosol dispersal. By mapping the phase space spanned by $Ec$, $De$, and $Oh_s$, we reveal three distinct flow regimes: (i) jets forming droplets, (ii) jets without droplet formation, and (iii) absence of jet formation. Our results elucidate the mechanisms underlying aerosol suppression versus fine spray formation in polymeric liquids, with implications for pathogen transmission and industrial processes involving viscoelastic fluids.
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