The intricate nature of non-Newtonian fluid rheology has raised notable attention, particularly in gas–liquid systems, where the dispersed bubbles may generate shear forces and change the shear-dependent viscosity of the surrounding liquid. While the effective shear rate, , is commonly used to approximate the shear-thinning viscosity around spherical bubbles, deviations may arise for deformed bubbles present in real systems. This work combines laboratory experiments and numerical simulations to investigate the evolution of a single rising bubble in three different systems: water, glycerol/water solutions characterizing viscous-Newtonian systems, and carboxymethyl cellulose (CMC) aqueous solutions exhibiting shear-thinning. The experiment was performed with bubble sizes of using imaging techniques. The measured fluid rheology is modeled by the Carreau model, and used in 3D direct numerical simulations based on a diffuse interface approach. The shear-thinning behaviors are found to increase the bubble terminal velocity through two distinct mechanisms: reducing the apparent viscosity around the bubble and promoting the bubble deformation. The extent of the shear-thinning effect depends on the three dominating regimes under which different rheology parameters play a significant role. Finally, empirical models for bubble terminal velocity and drag coefficient are evaluated using two shear-thinning viscosity estimations, based on the effective shear rate and the average shear-thinning viscosity near the bubble interface. The good agreement between experimental and simulation results validates the proposed models.

中文翻译：

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牛顿和非牛顿流体中单个气泡的动力学：实验和模拟方法

非牛顿流体流变学的复杂性质引起了人们的广泛关注，特别是在气液系统中，分散的气泡可能产生剪切力并改变周围液体的剪切力依赖性粘度。虽然有效剪切速率 通常用于近似球形气泡周围的剪切稀化粘度，但实际系统中存在的变形气泡可能会出现偏差。这项工作结合了实验室实验和数值模拟，研究了三个不同系统中单个上升气泡的演变：水、表征粘性牛顿系统的甘油/水溶液以及表现出剪切稀化的羧甲基纤维素 (CMC) 水溶液。使用成像技术以气泡尺寸进行实验。测量的流体流变学通过 Carreau 模型进行建模，并用于基于扩散界面方法的 3D 直接数值模拟。研究发现剪切稀化行为通过两种不同的机制来增加气泡终端速度：降低气泡周围的表观粘度并促进气泡变形。剪切稀化效应的程度取决于三种主要状态，在这三种状态下，不同的流变参数发挥重要作用。最后，基于气泡界面附近的有效剪切速率和平均剪切稀化粘度，使用两种剪切稀化粘度估计来评估气泡终端速度和阻力系数的经验模型。实验和模拟结果之间的良好一致性验证了所提出的模型。