title: Finite-size effects lead to supercritical bifurcations in turbulent rotating Rayleigh-Bénard convection.
abstract: In turbulent thermal convection in cylindrical samples with an aspect ratio Γ≡D/L (D is the diameter and L the height), the Nusselt number Nu is enhanced when the sample is rotated about its vertical axis because of the formation of Ekman vortices that extract additional fluid out of thermal boundary layers at the top and bottom. We show from experiments and direct numerical simulations that the enhancement occurs only above a bifurcation point at a critical inverse Rossby number 1/Ro(c), with 1/Ro(c)∝1/Γ. We present a Ginzburg-Landau-like model that explains the existence of a bifurcation at finite 1/Ro(c) as a finite-size effect. The model yields the proportionality between 1/Ro(c) and 1/Γ and is consistent with several other measured or computed system properties.
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106, USA.
authors.forename: Stephan
authors.initials: S
authors.lastname: Weiss
authors.forename: Richard J A M
authors.initials: RJ
authors.lastname: Stevens
authors.forename: Jin-Qiang
authors.initials: JQ
authors.lastname: Zhong
authors.forename: Herman J H
authors.initials: HJ
authors.lastname: Clercx
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.forename: Guenter
authors.initials: G
authors.lastname: Ahlers