title: Ultimate regime of high Rayleigh number convection in a porous medium.
abstract: Well-resolved direct numerical simulations of 2D Rayleigh-Bénard convection in a porous medium are presented for Rayleigh numbers Ra≤4×10(4) which reveal that, contrary to previous indications, the linear classical scaling for the Nusselt number, Nu~Ra, is attained asymptotically. The flow dynamics are analyzed, and the interior of the vigorously convecting system is shown to be increasingly well described as Ra→∞ by a simple columnar "heat-exchanger" model with a single horizontal wave number k and a linear background temperature field. The numerical results are approximately fitted by k~Ra(0.4).
authors.affiliation: Institute of Theoretical Geophysics, DAMTP, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA, United Kingdom.
authors.forename: Duncan R
authors.initials: DR
authors.lastname: Hewitt
authors.forename: Jerome A
authors.initials: JA
authors.lastname: Neufeld
authors.forename: John R
authors.initials: JR
authors.lastname: Lister