Flow reversals in thermally driven turbulence.
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.
Sugiyama
Kazuyasu
K
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.
Ni
Rui
R
Stevens
Richard J A M
RJ
Chan
Tak Shing
TS
Zhou
Sheng-Qi
SQ
Xi
Heng-Dong
HD
Sun
Chao
C
Grossmann
Siegfried
S
Xia
Ke-Qing
KQ
Lohse
Detlef
D