The prevention of hydrodynamic instabilities can lead to important insights for understanding the instabilities’ underlying dynamics. The Rayleigh-Taylor instability that arises when a dense fluid sinks into and displaces a lighter one is particularly difficult to arrest. By preparing a density inversion between two miscible fluids inside the thin gap separating two flat plates, we create a clean initial stationary interface. Under these conditions, we find that the instability is suppressed below a critical plate spacing. With increasing spacing, the system transitions from the limit of stability where mass diffusion dominates over buoyant forces, through a regime where the gap sets the wavelength of the instability, to the unconfined regime governed by the competition between buoyancy and momentum diffusion. Our study, including experiment, simulation, and linear stability analysis, characterizes all three regimes of confinement and opens new routes for controlling mixing processes.

防止水动力不稳定性可以导致重要的见解，以了解不稳定性的潜在动力。当稠密的流体沉入并置换较轻的流体时出现的瑞利-泰勒不稳定性特别难以阻止。通过在分隔两个平板的细间隙内的两个可混溶流体之间准备密度反演，我们创建了一个干净的初始固定界面。在这些条件下，我们发现不稳定性被抑制在临界板间距以下。随着间距的增加，系统从质量扩散在浮力上占主导地位的稳定极限过渡到通过间隙确定不稳定波长的状态，过渡到由浮力和动量扩散之间的竞争所支配的不受限制的状态。我们的研究，包括实验，