Mean Flow Generation by Two-Dimensional Roll Convection
Abstract
Fluid convection often gives rise to the formation of large-scale mean flows coexisting with the convective motion. This phenomenon is observed in both 2D numerical simulations (Thompson, 1970) and 3D laboratory experiments (Krishnamurti and Howard, 1981). In both cases, the mean flow forms in a periodic domain so that support against diffusion must be provided by up-gradient momentum fluxes. In two dimensions, convection drives the jet formation responsible for the transition from the low to high confinement state in tokamak plasmas. In three dimensions, spontaneous reorientation of a convectively driven large-scale flow in the Earth's interior has been suggested as a mechanism for the reversal of the Earth's magnetic field. In this contribution, the mechanism of mean flow generation in two-dimensional Rayleigh-Bénard convection is analyzed using a quasilinear (mean-field) approach. Previous theoretical models (such as Hermiz et al., 1995) predict the existence of a parameter range in which mean flow formation is prevented by vertical vorticity advection. The quasilinear system, on the other hand, predicts that mean flow formation occurs under all parameter conditions. The reason for this discrepancy is explained, and the mean flow dynamics of the quasilinear model are further explored and tested for robustness using the fully nonlinear equations of motion.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMNG23A1549F
- Keywords:
-
- 3215 MATHEMATICAL GEOPHYSICS / Instability analysis;
- 3314 ATMOSPHERIC PROCESSES / Convective processes;
- 3367 ATMOSPHERIC PROCESSES / Theoretical modeling;
- 4410 NONLINEAR GEOPHYSICS / Bifurcations and attractors