Steady Displacement of Long Gas Bubbles in Channels and Tubes Filled by a Bingham Fluid.
Steady Displacement of Long Gas Bubbles in Channels and Tubes Filled by a Bingham Fluid.
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宾汉流体填充的通道和管中长气泡的稳定位移。
DOI：
10.1103/physrevfluids.3.013302
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发表时间：
2018
影响因子：
2.7
通讯作者：
Grotberg,JamesB
中科院分区：
文献类型：
--
作者：
Zamankhan,Parsa;Takayama,Shuichi;Grotberg,JamesB
宾汉流体在von Mise应力阈值(屈服应力)以下表现为固体，高于该阈值则表现为牛顿流体。它们的特征是一个无量纲参数，宾汉数(Bn)，它是屈服应力与特征粘性应力的比率。本文数值研究了有限尺寸气泡在平面二维流道和宾汉流体填充轴对称管内的非惯性定常运动。宾汉数Bn在范围内，其中是牛顿情况，而毛细管数，即特征粘性力与表面张力的比率，具有值和0.25。所有轴对称和2D气泡的体积对于所有参数选择都是相同的，并且足够大，以使气泡与通道、管高和直径相比是长的。宾汉流体本构方程用正则化方程近似。在运动过程中，气泡界面被静态液膜与壁面隔开。由管子半径(轴对称)和通道高度的一半(2D)缩放的油膜厚度是无因次油膜厚度。结果表明，增加Bn首先导致增加，但轮廓Bn可以是单调或非单调取决于钙值和二维或轴对称组态。屈服应力还改变了气泡前后的形状，抑制了气泡后部的毛细管波。屈服应力增加了壁面切应力及其梯度的大小，因此增加了应用于肺粘液塞时上皮细胞损伤的可能性。在气泡参照系中，屈服面的拓扑结构和流动形态随Ca和Bn的变化而显著不同。
Bingham fluids behave like solids below a von Mises stress threshold, the yield stress, while above it they behave like Newtonian fluids. They are characterized by a dimensionless parameter, Bingham number (Bn), which is the ratio of the yield stress to a characteristic viscous stress. In this study, the noninertial steady motion of a finite-size gas bubble in both a plane two-dimensional (2D) channel and an axisymmetric tube filled by a Bingham fluid has been studied numerically. The Bingham number, Bn, is in the range, whereis the Newtonian case, while the capillary number, which is the ratio of a characteristic viscous force to the surface tension, has values, and 0.25. The volume of all axisymmetric and 2D bubbles has been chosen to be identical for all parameter choices and large enough for the bubbles to be long compared to the channel, tube height, and diameter. The Bingham fluid constitutive equation is approximated by a regularized equation. During the motion, the bubble interface is separated from the wall by a static liquid film. The film thickness scaled by the tube radius (axisymmetric) and half of the channel height (2D) is the dimensionless film thickness,. The results show that increasing Bn initially leads to an increase in; however, the profileversus Bn can be monotonic or nonmonotonic depending on Ca values and 2D or axisymmetric configurations. The yield stress also alters the shape of the front and rear of the bubble and suppresses the capillary waves at the rear of the bubble. The yield stress increases the magnitude of the wall shear stress and its gradient and therefore increases the potential for epithelial cell injuries in applications to lung airway mucus plugs. The topology of the yield surfaces as well as the flow pattern in the bubble frame of reference varies significantly by Ca and Bn.