Shear-driven flow can be either imposed by a pressure gradient or through the implementation of moving walls. A simple way to realize this is plane Couette flow, where the top and bottom wall move in opposite directions to shear the flow while keeping the mean flow velocity neutral. The shearing motion increases the momentum exchange and cause large scale structures to emerge, which fill the whole channel. Solely buoyancy-driven convection, such as Rayleigh-Bénard flow, is used as unstable flow stratification to enforce thermal convection from a lower, heated plate to a higher, cooled plate. This can be the numerical origin for phenomena such as ocean dynamics, clouds and atmospheric physics in general. The main drive for the heat exchange are large scale structures which are initiated by the motion of thermal plumes.
While these two phenomena separately are very well studied and understood, their combination is far less researched. The visualization reveals the final outcome of clear large scale meandering structures which are significantly more prominent than the large structures already observed in plane Couette flow. Depending on the choice of control parameters, these structures can be varied in thickness, number and wavelength. This type of flow, where buoyancy and shear interact, is a vital process in the area of fluid dynamics and the foundation for many mechanisms in nature.