Numerical insight into flow structure in ultraturbulent thermal convection.

Very large eddy simulations of high-aspect-ratio unbounded Rayleigh-Bénard convection for Pr=0.71 over a 10-decade range of Rayleigh numbers (Ra=10(5)-10(15)) reveal a consolidation and dramatic thinning of the wall boundary layer with an increase in the Ra number. The fingerlike plumes between planform structures become also thinner, more distant, but much more vigorous. The Ra exponent in the Nu proportional to Ra(n) correlation follows n approximately 0.31 scaling, but n begins to increase gradually above Ra=10(13). However, no trend towards "crossing" of the thermal and hydrodynamic boundary layers is observed.