14:15 〜 14:30
[MIS12-03] 水平温度勾配印加による熱乱流の過渡的変化
キーワード：熱乱流、水平対流、傾圧トルク、流れ構造
Various studies have conducted on Rayleigh-Bénard convection (RBC) caused by vertical temperature gradient as a basis for heat transfer and turbulence study. In addition, there exists horizontal convection (HC) driven by the baroclinic torque due to the imposition of a horizontal temperature gradient. The flow resulting from the superposition of RBC with HC is of fundamental interest and has potentially important applications in the environment.
We experimentally investigated transient behaviors from RBC to HC by imposing horizontal temperature gradients on forcing boundaries in addition to the vertical unstable temperature gradients. A rectangular vessel with an aspect ratio of two was used, and fixed vertical and horizontal temperature differences, 10°C, were imposed on the test fluid, water. Visualization of the temperature field and velocity distribution measurement were performed using thermosensitive liquid crystal particles as tracer particles and as temperature visualizer. We continuously observed flow fields for 120 min after imposing the horizontal temperature gradients to achieve quasi-steady states. Before the system being influenced by the horizontal forcing, thermal boundary layers were detached intermittently as thermal plumes leading to large-scale circulations (LSCs), which are variable in size and rotation direction. A LSC occupying the entire fluid layer was formed quickly, approximately 180 seconds after the horizontal forcing.
Instantaneous velocity vector fields were obtained by particle tacking velocimetry with nearest neighbor algorithm to quantify the transient behavior. Roughly 20,000 vectors were obtained on each snapshot of the sequential images. We thus calculated the probability density function of the velocity distributions and the angular momentum around the vessel center. Examining these time variations indicated that the LSCs in the thermal turbulence are modified by the horizontal temperature difference in time scales comparable to couple of circulation time scale of the LSCs.
We experimentally investigated transient behaviors from RBC to HC by imposing horizontal temperature gradients on forcing boundaries in addition to the vertical unstable temperature gradients. A rectangular vessel with an aspect ratio of two was used, and fixed vertical and horizontal temperature differences, 10°C, were imposed on the test fluid, water. Visualization of the temperature field and velocity distribution measurement were performed using thermosensitive liquid crystal particles as tracer particles and as temperature visualizer. We continuously observed flow fields for 120 min after imposing the horizontal temperature gradients to achieve quasi-steady states. Before the system being influenced by the horizontal forcing, thermal boundary layers were detached intermittently as thermal plumes leading to large-scale circulations (LSCs), which are variable in size and rotation direction. A LSC occupying the entire fluid layer was formed quickly, approximately 180 seconds after the horizontal forcing.
Instantaneous velocity vector fields were obtained by particle tacking velocimetry with nearest neighbor algorithm to quantify the transient behavior. Roughly 20,000 vectors were obtained on each snapshot of the sequential images. We thus calculated the probability density function of the velocity distributions and the angular momentum around the vessel center. Examining these time variations indicated that the LSCs in the thermal turbulence are modified by the horizontal temperature difference in time scales comparable to couple of circulation time scale of the LSCs.