In this article, we explore the development and mixing that results from Rayleigh–Taylor instability between two layers. Unlike the classical problem, one of the two layers initially has a stable density stratification, while the density of the fluid in the other is uniform. The results presented here are from low Atwood number experiments with incompressible fluids, although there is an analogy between this case and low accelerations of compressible fluids that result in hydrostatic gradients that differ significantly. In both scenarios, the instability growth is asymmetric. For the present case, mixing will occur throughout the region initially occupied by the layer of uniform density but, depending on the strength of the stratification compared with the density difference across the initial Rayleigh–Taylor-unstable interface, the mixing may be arrested by the stratification before it reaches the lower boundary of the domain. We propose a simple model for the growth of the instability and see that it captures the qualitative behaviour. The final state comprises a weakly stratified layer bounded on one side by the remnant of the initially stratified layer. The structure of this weak stratification is seen to be consistent with the idea of maximal configurational entropy for the mixing zone. Ultimately, the efficiency of this mixing process is found to follow the pattern expected for ‘perfect mixing’ equivalent, but achieves only 94% of the corresponding value.

在本文中，我们探讨了由两层之间的瑞利-泰勒不稳定性引起的发展和混合。与经典问题不同，两层中的一层最初具有稳定的密度分层，而另一层中的流体密度是均匀的。此处给出的结果来自不可压缩流体的低阿特伍德数实验，尽管在这种情况与可压缩流体的低加速度之间存在类比，导致流体静力梯度差异显着。在这两种情况下，不稳定的增长都是不对称的。在目前情况下，混合将在整个最初由均匀密度层占据的区域中发生，但是取决于分层强度与初始瑞利-泰勒-不稳定界面上的密度差相比，混合可能在到达畴的下边界之前被分层阻止。我们为不稳定的增长提出了一个简单的模型，并看到它捕获了定性行为。最终状态包括一个弱分层层，该薄分层层的一侧由初始分层层的残余物界定。可以看出这种弱分层的结构与混合区最大构型熵的思想是一致的。最终，发现该混合过程的效率遵循“完全混合”等效条件所预期的模式，但仅达到相应值的94％。最终状态包括一个弱分层层，该薄分层层的一侧由初始分层层的残余物界定。可以看出这种弱分层的结构与混合区最大构型熵的思想是一致的。最终，发现该混合过程的效率遵循“完全混合”等效条件所预期的模式，但仅达到相应值的94％。最终状态包括一个弱分层层，该薄分层层的一侧由初始分层层的残余物界定。可以看出这种弱分层的结构与混合区最大构型熵的思想是一致的。最终，发现该混合过程的效率遵循“完全混合”等效条件所预期的模式，但仅达到相应值的94％。