title: Flow reversals in thermally driven turbulence.
abstract: We analyze the reversals of the large-scale flow in Rayleigh-Bénard convection both through particle image velocimetry flow visualization and direct numerical simulations of the underlying Boussinesq equations in a (quasi-) two-dimensional, rectangular geometry of aspect ratio 1. For medium Prandtl number there is a diagonal large-scale convection roll and two smaller secondary rolls in the two remaining corners diagonally opposing each other. These corner-flow rolls play a crucial role for the large-scale wind reversal: They grow in kinetic energy and thus also in size thanks to plume detachments from the boundary layers up to the time that they take over the main, large-scale diagonal flow, thus leading to reversal. The Rayleigh vs Prandtl number space is mapped out. The occurrence of reversals sensitively depends on these parameters.
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology, Impact and MESAþ Institutes & Burgers Center for Fluid Dynamics,University of Twente, 7500AE Enschede, The Netherlands.
authors.forename: Kazuyasu
authors.initials: K
authors.lastname: Sugiyama
authors.forename: Rui
authors.initials: R
authors.lastname: Ni
authors.forename: Richard J A M
authors.initials: RJ
authors.lastname: Stevens
authors.forename: Tak Shing
authors.initials: TS
authors.lastname: Chan
authors.forename: Sheng-Qi
authors.initials: SQ
authors.lastname: Zhou
authors.forename: Heng-Dong
authors.initials: HD
authors.lastname: Xi
authors.forename: Chao
authors.initials: C
authors.lastname: Sun
authors.forename: Siegfried
authors.initials: S
authors.lastname: Grossmann
authors.forename: Ke-Qing
authors.initials: KQ
authors.lastname: Xia
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse