Convectively driven shear and decreased heat flux

摘要: We report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh-B\'enard convection, focusing its ability to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($Pr$) between 1 and 10 simulated here, this shear can be induced by raising Rayleigh number ($Ra$) sufficiently, we explore resulting convection for $Ra$ up $10^{10}$. When present in our simulations, sheared mean accounts a large fraction total kinetic energy, tends towards unity as $Ra\to\infty$. The helps disperse convective structures, it reduces vertical heat flux; parameter regimes where one state with without are both stable, Nusselt smaller grows more slowly $Ra$. $Pr\lesssim2$, undergoes strong global oscillations long timescales, transport occurs bursts. numbers, time-averaged over these bursts, vary non-monotonically $Pr=1$. $Pr\gtrsim3$, does not burst, sustained at all times. then grow roughly powers $Ra$, but growth rates slower than any previously reported shear. find proportionally $Ra^{0.077}$ when $Pr=3$ $Ra^{0.19}$ $Pr=10$. Analogies tokamak plasmas described.