[M-IS21] Geophysical fluid dynamics-Transfield approach to geoscience

[MIS21-P01] Transient and statistical characteristics of thermal turbulence modified by horizontal convection

*Kaito Yoda¹, Yuji Tasaka², Daisuke Noto³, Takatoshi Yanagisawa⁴, Yuichi Murai² (1.Graduate School of Engineering, Hokkaido University, 2.Faculty of Engineering, Hokkaido University, 3.University of Pennsylvania, 4.Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology)

Keywords:Thermal turbulence, Horizontalo conveciton , Baroclinic tourque, Flow structure

Rayleigh-Bénard convection (RBC) driven by vertical temperature gradient between parallel plates have been studied as a basis for heat transfer and turbulence study. It is also known that horizontal convection (HC) driven by the baroclinic torque due to a horizontal temperature gradient is a canonical problem. The flow resulting from the superposition of RBC and HC is of fundamental interest and is of significant relevance in natural and industrial environments. We revealed that turbulent RBC driven solely by the vertical temperature gradient is altered by imposing the horizontal temperature gradient, resulting in a single large-scale circulation (LSC) irrespective of the boundary conditions. We further study the statistical characteristics of the transition from RBC to HC-dominant RBC through laboratory experiments. For the experiment, a rectangular vessel with an aspect ratio of two were utilized, and 16 variations of vertical and horizontal temperature differences were investigated. Temperature field visualization and velocity field measurement were performed using thermosensitive liquid crystal particles as tracer particles. Instantaneous velocity vector fields were obtained from the particle images by particle tacking velocimetry with nearest neighbor algorithm to quantify the transient behavior. We calculated the angular momentum and kinetic energy to investigate the effect of horizontal temperature gradients on the global structure and the mixing efficiency due to convection. As a result, it was found that the horizontal temperature gradient causes a large change in angular momentum, forming a single circulating flow, and that the mixing efficiency increases due to the increase in kinetic energy. We introduced a Rayleigh number that considers both vertical and horizontal temperature differences, and by organizing the values of kinetic energy under each set of conditions, we were able to organize the phenomenon of this combinational convection.