Prandtl number dependence of flow topology in quasi-two-dimensional turbulent Rayleigh-Bénard convection

To date, a comprehensive understanding of the influence of the Prandtl number on flow topology in turbulent Rayleigh-Bénard convection (RBC) remains elusive. In this study, we present an experimental investigation into the evolution of flow topology in quasi-two-dimensional turbulent RBC with and. Particle image velocimetry (PIV) measurements reveal the flow transitions from multiple-roll state to single-roll state with increasing, and the transition is hindered with increasing, i.e. the transitional Rayleigh number increases with. We mapped out a phase diagram on the flow topology change on and, and identified the scaling of on: in the low range, and in the high range. The scaling in the low range is consistent with the model of balance of energy dissipation time and plume travel time that we proposed in our previous study, while the scaling in the high range implies a new governing mechanism. For the first time, the scaling of on and is acquired through full-field PIV velocity measurement,. We also propose that increasing horizontal velocity promotes the formation of the large-scale circulation (LSC), especially for the high case. Our proposal was verified by achieving LSC through introducing horizontal driving force by tilting the convection cell with a small angle.