Changes in the boundary-layer structure at the edge of the ultimate regime in vertical natural convection

Abstract

In thermal convection for very large Rayleigh numbers , the thermal and viscous boundary layers are expected to undergo a transition from a classical state to an ultimate state. In the former state, the boundary-layer thicknesses follow a laminar-like Prandtl-Blasius-Polhausen scaling, whereas in the latter, the boundary layers are turbulent with logarithmic corrections in the sense of Prandtl and von Kármán. Here, we report evidence of this transition via changes in the boundary-layer structure of vertical natural convection (VC), which is a buoyancy-driven flow between differentially heated vertical walls. The numerical dataset spans values from to and a constant Prandtl number value of . ..