English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Vertical convection is investigated using direct numerical simulations over awide range of Rayleigh numbers $10^7\le Ra\le10^{14}$ with fixed Prandtl number$Pr=10$, in a two-dimensional convection cell with unit aspect ratio. It isfound that the dependence of the mean vertical centre temperature gradient $S$on $Ra$ shows three different regimes: In regime I ($Ra \lesssim5\times10^{10}$), $S$ is almost independent of $Ra$; In the newly identifiedregime II ($5\times10^{10} \lesssim Ra \lesssim 10^{13}$), $S$ first increaseswith increasing $Ra$ (regime ${\rm{II}}_a$), reaches its maximum and thendecreases again (regime ${\rm{II}}_b$); In regime III ($Ra\gtrsim10^{13}$), $S$again becomes only weakly dependent on $Ra$, being slightly smaller than inregime I. The transitions between diffeereent regimes are discussd. In thethree different regimes, significantly different flow organizations areidentified: In regime I and regime ${\rm{II}}_a$, the location of the maximalhorizontal velocity is close to the top and bottom walls; However, in regime${\rm{II}}_b$ and regime III, banded zonal flow structures develop and themaximal horizontal velocity now is in the bulk region.  The different flow organizations in the three regimes are also reflected inthe scaling exponents in the effective power law scalings $Nu\sim Ra^\beta$ and$Re\sim Ra^\gamma$. In regime I, the fitted scaling exponents($\beta\approx0.26$ and $\gamma\approx0.51$) are in excellent agreement withthe theoretical predication of $\beta=1/4$ and $\gamma=1/2$ for laminar VC(Shishkina, {\it{Phys. Rev. E.}} 2016, 93, 051102). However, in regimes II andIII, $\beta$ increases to a value close to 1/3 and $\gamma$ decreases to avalue close to 4/9. The stronger $Ra$ dependence of $Nu$ is related to theejection of plumes and larger local heat flux at the walls.

Regime transitions in thermally driven high-Rayleigh number vertical convection