[M-IS12] Geophysical fluid dynamics-Transfield approach to geoscience

[MIS12-P02] Thermal convection in enclosed narrow geometries

*Takatoshi Yanagisawa^1,3, Masanori Kameyama^2,1, Sota Takano³, Daisuke Noto⁴, Yuji Tasaka^3,1, Takehiro Miyagoshi¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.Geodynamics Researth Center, Ehime University, 3.Faculty of Engineering, Hokkaido University, 4.University of Pennsylvania)

Keywords:convection, narrow gap, oscillation, numerical simulation

We investigated convection patterns in three-dimensional rectangular geometries by numerical simulations. The aspect ratios of both x and y horizontal directions to that of vertical direction z are the parameters to characterize the geometry. Convection is driven by the fixed temperature difference between the top and bottom boundaries, and all sidewalls are insulating. When the aspect ratio in y direction (Ly) is small, it corresponds to a model of water or magma circulation in a vertical gap. When that of x (Lx) is also small, it is a model of vertically elongated pipe. We treated Boussinesq fluid by our numerical code originally developed for mantle convection simulations. We check Ly dependence of the critical Rayleigh number (Ra) for the onset of convection. The critical value increases for smaller Ly, and approaches to that of Hele-Shaw cell. With the increase of Ra from the critical value, the horizontal scale of convection roll gets shorter, that is, the wave number of the pattern increases. On the transition, we observed emergence of oscillatory small circulations at four corners of the x-z plane. These oscillatory corner circulations emerges however large Lx is, and then the enclosed volume is divided into central steady flow region and time-dependent flow regions near the sidewalls. We investigated the feature of these oscillatory corner circulations.