Plume dynamics in rotating Rayleigh-Benard convection

Turbulent Rayleigh-Benard convection is characterized by the presence of intense coherent structures called plumes. With additional system rotation along an axis parallel to gravity, individual plumes can merge together to form larger thermal structures. In this paper, we propose an efficient way to quantify plume merging using three accessible statistics: plume vorticity, plume number and plume area. Using this approach, we show that plume merging is more intense for moderate values of the Rossby number, around Ro approximate to 1. Merging is spatially localized near boundary layers, determining what we call the ``merging region{''}. Inside this region, vertical heat transport by individual plumes is enhanced. Outside the merging region, on the other hand, rotating plumes transport less heat than in the non-rotating case. Since the total heat transport is enhanced by rotation in the turbulent regime explored here, this implies that outside the merging region the vortical structures of background turbulence transport heat more effectively than in the non-rotating case. (C) 2016 Elsevier B.V. All rights reserved.