We experimentally inject silicone oil into the mixture of oil and noncolloidal particles inside a Hele-Shaw cell, to investigate the connection between miscible fingering and the interfacial structure that develops inside the thin gap. Previous studies with pure fluids have demonstrated that the onset of miscible fingering coincides with the transition from a smooth tonguelike structure to a sharp front between invading and defending fluids inside the gap. Our current experiments with suspensions reveal the same general behavior at the onset of miscible fingering, which we capture qualitatively using a lubrication model. However, distinct from the pure liquid counterpart, we observe changes in the interfacial structures inside the gap as the ratio of the gap thickness to particle diameter is systematically varied. We demonstrate that the particle dynamics inside the thin gap may alter interfacial structures even within the continuum limit, which lead to changes in morphologies of miscible fingering. The results of our study suggest a potential use of the wall confinement to control hydrodynamic instabilities in suspensions.

中文翻译：

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粒子诱导的混溶指法：连续谱极限

我们通过实验将硅油注入Hele-Shaw池中的油和非胶体颗粒的混合物中，以研究可溶指与薄间隙内部形成的界面结构之间的联系。以前对纯液体的研究表明，可混溶指法的发作与间隙内入侵和防御液体之间从光滑的舌状结构过渡到锋利的前锋相吻合。我们目前的悬架实验表明，在混合指法发生时，我们具有相同的一般行为，我们使用润滑模型进行定性捕获。但是，与纯液体相反，随着间隙厚度与粒径的比率系统地变化，我们观察到间隙内部界面结构的变化。我们证明，即使在连续范围内，细间隙内部的粒子动力学也可能会改变界面结构，从而导致混合指法的形态发生变化。我们的研究结果表明，限制围墙的潜在用途是控制悬浮液的流体动力不稳定性。