Formation of superswells and domes in layered turbulent convection systems

Superswells and domes – large-scale, persistent interface deformations – are key features in geophysical and multiphase systems driven by thermal convection. These structures often emerge in layered convective systems, such as Earth’s mantle or two-fluid industrial processes, where buoyancy contrasts and fluid properties create complex interface dynamics. However, the physical mechanisms governing the formation of these structures remain poorly understood. Here, we use high-resolution direct numerical simulations of two-layer Rayleigh–Bénard convection to investigate how the Prandtl number (Pr) and buoyancy number (B) govern transitions in interfacial morphology. At a fixed Rayleigh number (Ra), we identify three distinct regimes: stratified convection at high B, where compositional buoyancy suppresses interfacial motion; an interfacial fragmentation regime at low Pr and B, driven by inertial–thermal buoyant balance; and a transitional dome-forming regime within a Pr -dependent range, where viscous and buoyant forces deform the interface into coherent, superswell-like structures. A theoretical phase diagram predicts these transitions and agrees well with simulation results. These findings provide mechanistic insight into interfacial phase behaviour in thermally driven flows, offering a framework that links geophysical surface features with underlying convective dynamics and informing the control of interfacial morphology in complex multiphase systems.