Analysis of coherent structures in Rayleigh–Bénard convection

Using direct numerical simulation, we investigate characteristics of coherent structures in Rayleigh–Bénard convection in a soft turbulence regime. The role of thermal plumes, essential structures in Rayleigh–Bénard convection, is studied by splitting flow regimes into thermal plume and background by investigating joint probability density function (PDF) of invariants of velocity gradient tensor. The contribution to thermal dissipation rate by these two regions is analysed separately. Through the joint PDF of invariants, we also examine the thermal effect on velocity structures.