Physical mechanisms to induce flow-transitions and to sustain turbulence

2019 Fiscal Year Final Research Report

• Project/Area Number: 15K05220
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Mathematical physics/Fundamental condensed matter physics
• Research Institution: Doshisha University
• Principal Investigator: Mizushima Jiro 同志社大学, 研究開発推進機構, 嘱託研究員 (70102027)
• Project Period (FY): 2015-04-01 – 2020-03-31
• Keywords: 流体 / 数理物理 / 計算物理 / 力学系 / 非線形物理

Outline of Final Research Achievements

In the present research project, I have clarified physical mechanisms underlying instability and transitions of several major flows. The induction mechanisms of oscillatory thermal convection in two-component fluid and also in double-layered fluid were elucidated by evaluation of torques acting on the fluid. The appearance of a large-scale vortex, so-called 'bathtub vortex', in a rectangular vessel was found to be caused by pressure force exerted by the lateral walls. The flow through a channel with an expanded section was found to become oscillatory due to 'trapped instability’. The driving mechanism of Tollmien-Schlichting waves appearing in transition of the plane Poiseuille flow was found to be explained by mutual interactions between two flow fields defined by the real and imaginary parts of the eigen functions by analyzing the torques exerting on each flow field. From these investigations, I obtained many fruitful results and published or scientific papers to prominent journals.

Free Research Field

数物系科学

Academic Significance and Societal Importance of the Research Achievements

流れの安定性は自然科学だけでなく工学的にも重要であるが、不安定性が生じる機構についてはほとんど調べられてこなかった。本研究計画では流れの不安定性を渦の生成という観点から見直し、不安定性による新たな振動と流れパターンの発生に着目して、代表的な流れの不安定性発生機構を明らかにした。特に、平面ポワズイユ流の不安定機構の解明の手法は幅広い分野の流れに応用できるので、今後の乱流遷移の研究に重要な研究方法となると期待される。矩形断面容器中の大規模渦の発生機構の解明は「バスタブ渦の発生原理」として、広く中学生、高校生、教員だけでなく、一般の市民の興味を集め、台風や竜巻などへの興味を引き出すことができた。