2023-05-15 ニューヨーク大学 (NYU)
◆この研究では、温度差によって生じるレイリー・ベナール対流に焦点を当てました。実験では、円筒形の容器に水を入れて加熱し、乱流の流れと固体の相互作用を観察しました。驚くべきことに、乱流と固体の間で円滑な回転が観察されました。
◆この研究は、地球の内部核と液体核の相互作用に触発されたものであり、乱流が固体との相互作用によって制御されることを示しています。また、熱対流の力が地球内部で重要な役割を果たしている可能性を示唆しています。
＜関連情報＞
- https://www.nyu.edu/about/news-publications/news/2023/may/physicists-take-the-temperature-of-fluid-flows-and-discover-new-.html
- https://www.pnas.org/doi/10.1073/pnas.2217705120
熱対流と自由体浸漬の大規模流れの持続的なコロケーションを発見 Persistent corotation of the large-scale flow of thermal convection and an immersed free body
Kaizhe Wang and Jun Zhang
Proceedings of the National Academy of Sciences Published:May 15, 2023
Significance
Symmetry-breaking bifurcations are omnipresent in nature and in artificial settings, from quantum physics to dynamic systems, and can also be found in many fluid–structure interactions. In this study, we investigate the interplay between a freely rotatable body and thermal convective flows in a table-top experiment. We find a surprising and persistent corotation of the free body together with the main flow structures. The two corotational solutions, one clockwise and the other counterclockwise, result from a symmetry-breaking bifurcation of the coupled system, powered merely by the turbulent convective flow. We successfully interprets the mechanism of the fluid–structure interaction and explains the stochastic reversals between two corotational directions.
Abstract
Inspired by the superrotation of the Earth’s solid core, we investigate the dynamics of a free-rotating body as it interacts with the large-scale circulation (LSC) of the Rayleigh–Bénard thermal convection in a cylindrical container. A surprising and persistent corotation of both the free body and the LSC emerges, breaking the axial symmetry of the system. The corotational speed increases monotonically with the intensity of thermal convection, measured by the Rayleigh number Ra, which is proportional to the temperature difference between the heated bottom and cooled top. The rotational direction occasionally and spontaneously reverses, occurring more frequently at higher Ra. The reversal events follow a Poisson process; it is feasible that flow fluctuations randomly interrupt and reestablish the rotation-sustaining mechanism. This corotation is powered by thermal convection alone and promoted by the addition of a free body, enriching the classical dynamical system.
