Subcritical convection in rapidly rotating liquid metal spheres [article]

Nathanael Schaeffer, Elliot Kaplan, Philippe Cardin, Céline Guervilly, Jérémie Vidal
<span title="2017-11-20">2017</span> <i title="Figshare"> Figshare </i> &nbsp;
Planetary​ ​cores​ ​consist​ ​of​ ​liquid​ ​metals​ ​(low​ ​Prandtl​ ​number​ ​Pr)​ ​that​ ​convect​ ​as​ ​the​ ​core​ ​cools.Here​ ​we​ ​study​ ​nonlinear​ ​convection​ ​in​ ​a​ ​rotating​ ​(low​ ​Ekman​ ​number​ ​Ek)​ ​planetary​ ​core​ ​using​ ​a fully​ ​3D​ ​direct​ ​numerical​ ​simulation.​ ​At​ ​high​ ​rotation​ ​rate,​ ​the​ ​convection​ ​onsets​ ​in​ ​a​ ​turbulent state,​ ​and​ ​can​ ​be​ ​maintained​ ​well​ ​below​ ​the​ ​linear​ ​onset​ ​of​ ​convection​ ​(down​ ​to​ ​Ra=0.7​
more &raquo; ... ​​ ​in this​ ​study).We​ ​highlight​ ​the​ ​importance​ ​of​ ​the​ ​Reynolds​ ​stress,​ ​which​ ​is​ ​required​ ​for​ ​convection​ ​to​ ​subsist below​ ​the​ ​linear​ ​onset.​ ​In​ ​addition,​ ​the​ ​Péclet​ ​number​ ​is​ ​consistently​ ​above​ ​10​ ​in​ ​the​ ​strong branch.​​We​ ​further​ ​note​ ​the​ ​presence​ ​of​ ​a​ ​strong​ ​zonal​ ​flow​ ​that​ ​is​ ​nonetheless​ ​unimportant​ ​to the​ ​convective​ ​state.​​Our study​ ​suggests​ ​that,​ ​in​ ​the​ asymptotic​ ​regime​ ​of​ ​rapid​ ​rotation​ ​relevant for​ ​planetary​ ​interiors,​ ​thermal​ ​convection​ ​of​ ​liquid​ ​metals​ ​in​ ​a​ ​sphere​ ​onsets​ ​through​ ​a subcritical​ ​bifurcation.
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