泡沫绕圆形障碍物的二维流动：弹性、塑性和流动的局部测量
Two-dimensional flow of foam around a circular obstacle: local measurements of elasticity, plasticity and flow
摘要：
我们调查的二维流动的液体泡沫周围的圆形障碍物通过测量所有的本地字段来描述这种流动：速度，压力，气泡变形和重排。我们展示了我们的实验装置，一个准2D的“液体池”系统，是适应这些领域的确定：速度和气泡变形是很容易从2D电影测量，和压力可以通过利用这个系统的一个特定的功能，一个2D有效的压缩性测量。为了准确地描述气泡重排，我们提出了一个新的，张量描述。所有这些量都通过平均程序进行评估，我们证明场的波动本质上是随机的。在参考实验情况下，对流动进行了广泛的研究;在障碍物的尾流中，速度呈现出过冲，压力在前侧最大，在后侧最小。弹性形变和速度梯度的研究表明，活塞流和屈服区之间的过渡是平滑的。我们的张量描述T1 s突出其相关性与气泡变形和速度梯度。流动的一个显著特征，特别是在速度和T1再分配上，是泡沫弹性行为的显著不对称上游/下游特征。我们发现，结果不改变定性时，各种控制参数的变化，确定一个强大的准静态制度。这些结果进行了讨论的框架中的实际泡沫流变学文献，我们认为，它们构成了现有的流变模型的严峻考验，因为它们捕获的弹性，塑性和流体行为的泡沫。
英文摘要：
We investigate the two-dimensional flow of a liquid foam around circular obstacles by measuring all the local fields necessary to describe this flow: velocity, pressure, bubble deformations and rearrangements. We show how our experimental setup, a quasi-2D "liquid pool" system, is adapted to the determination of these fields: the velocity and bubble deformations are easy to measure from 2D movies, and the pressure can be measured by exploiting a specific feature of this system, a 2D effective compressibility. To describe accurately bubble rearrangements, we propose a new, tensorial descriptor. All these quantities are evaluated via an averaging procedure that we justify showing that the fluctuations of the fields are essentially random. The flow is extensively studied in a reference experimental case; the velocity presents an overshoot in the wake of the obstacle, the pressure is maximum at the leading side and minimal at the trailing side. The study of the elastic deformations and of the velocity gradients shows that the transition between plug flow and yielded regions is smooth. Our tensorial description of T1s highlight their correlation both with the bubble deformations and the velocity gradients. A salient feature of the flow, notably on the velocity and T1 repartition, is a marked asymmetry upstream/downstream, signature of the elastic behaviour of the foam. We show that the results do not change qualitatively when various control parameters vary, identifying a robust quasistatic regime. These results are discussed in the frame of the actual foam rheology literature, and we argue that they constitute a severe test for existing rheological models, since they capture both the elastic, plastic and fluid behaviour of the foam.
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