A study on edge of chaos using perturbation accompanying with artificial hair-pin vortices

2018 Fiscal Year Final Research Report

• Project/Area Number: 16H04260
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Fluid engineering
• Research Institution: Hokkaido University
• Principal Investigator: Tasaka Yuji 北海道大学, 工学研究院, 准教授 (00419946)
• Co-Investigator(Kenkyū-buntansha): 村井 祐一 北海道大学, 工学研究院, 教授 (80273001)
• Research Collaborator: NAKANO Naoto ; PEIXINHO Jorge ; BOX Finn ; MULLIN Tom
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 乱流遷移 / 流れ制御

Outline of Final Research Achievements

The present study investigated subcritical flow transitions in a pipe with hair-pin vortices as disturbances generated by a synthetic jet actuator, which is capable to control amplitude, frequency and number of the hair-pins. The experimental results indicated that the frequency and amplitude do no affect considerably the transition, but for small number of hair-pins, the transition clearly depends on the number of vortices. As other project in the study, trials to modify self-sustaining process of the local turbulence were performed by, for example, attachment of a bubble on the pipe wall. It works well to introduce relaminarization of the local turbulence and corresponding mechanism we considered is removing inflection points on the velocity profile at the trailing edge of the turbulence by flow winding and slip on the bubble surface.

Free Research Field

流体力学

Academic Significance and Societal Importance of the Research Achievements

流れの乱流遷移は，これまでの研究により，熱対流などのように段階的に遷移が進むモーダルな過程は理論や数値計算，実験などによりおおよそのそのメカニズムが解明されつつある．一方で，円管流れに代表される突発的な遷移（亜臨界遷移）については，Edge stateなど数理面での理解が進むものの，具体的な遷移過程，特により少ないエネルギーで乱流化異形成に導く最適攪乱の問題など，未だ明らかにされていないことが多い．本研究では，これまでの研究から最適攪乱としての機能を見込めるヘアピン渦列を，制御可能な条件で生成できるシンセティックジェットを用いて生成し，最適攪乱を探求する課題である．