Rayleigh-Bénard convection at Ra=10^7 and infinite Prandtl number

The 4x4x1 box initially at a temperature T=1/2 is subjected to T=1 at the bottom and T=0 at the top. The domain is periodic in both horizontal directions. The movie shows the evolution of two surface of iso-temperature, intermediate between 1/2 and that of the boundaries. Even though the Reynolds number is identically null (Stokes flow), the Péclet number is large, which makes the flow highly time-dependent. This situation of infinite-Prandtl-number convection is thought to apply to rocky or icy mantles of planetary objects.