Multi-layer Rayleigh–Taylor instability: Consequences for naturally occurring stratified mixing layers

The present study investigates the behavior of multi-layer Rayleigh–Taylor instability (RTI) and enstrophy transport in the flow using a three-dimensional computational framework. The dynamics of RTI are explored in a monotonically unstable stratified fluid system composed of air at different constant temperatures, initially separated by insulating partitions. Our results illustrate the formation of a multi-layer RTI system and the growth of convective mixing layers from interfaces between consecutive layers. The behavior of single-layer and multi-layer RTI is compared by considering the influence of Atwood numbers on growth and characteristics of the mixing layers. We found that the presence of multiple layers affects the onset and development of RTI. The merging of top layers leads to accelerated mixing layer growth, while the bottommost layer experiences early-stage RTI. Furthermore, we utilize the compressible enstrophy transport equation to characterize dominant mechanisms controlling the spatiotemporal evolution of the multi-layer RTI. The results highlight the significance of viscous and compressibility terms, especially in the center. In contrast, the vortex stretching term dominates near side walls for later stages of the RTI. These insights enrich the understanding of multi-layer RTI and its effects on enstrophy transport and mixing in unstably stratified fluid systems, providing valuable data for validating numerical methods and informing future research in related fields.