Plume structures in the hard‐turbulent regime of three‐dimensional infinite Prandtl number convection

Numerical simulations of three‐dimensional infinite Prandtl number thermal convection with Rayleigh number (Ra) up to 10⁸ are reported. Convection with Ra higher than 10⁷ is characterized by the appearance of disconnected thermal plumes. The smaller plumes are detached by the currents produced by the larger plumes. The low wavenumber portion of a thermal power spectrum near the boundary layer becomes flat at high Ra, while the spectrum measured in the interior shows a positive slope for low wavenumbers. Differences are found in the thermal spectra between 2D and 3D models.