Key vortical structure causing laminar-turbulent transition in a boundary layer disturbed by a short-duration jet

Joe Yoshikawa, Yu Nishio, Seiichiro Izawa, Yu Fukunishi

研究成果: Article査読

4 被引用数 (Scopus)

抄録

Numerical simulations are carried out to discover the flow structure that plays an important role in the laminar-turbulent transition process of a boundary layer on a flat plate. The boundary layer is destabilized by ejecting a short-duration jet from a hole in the surface. When the jet velocity is set to 20% of the uniform-flow velocity, a laminar-turbulent transition takes place, whereas in the 18% case, the disturbances created by the jet decay downstream. It is found that in both cases, hairpin vortices are generated; however, these first-generation hairpins do not directly cause the transition. Only in the 20% case does a new hairpin vortex of a different shape with wider distance between the legs appear. The new hairpin grows with time and evokes the generation of vortical structures one after another around it, turning the flow turbulent. It is found that the difference between the two cases is whether or not one of the first-generation hairpin vortices gets connected with the nearby longitudinal vortices. Only when the connection is successful is the new hairpin vortex with wider distance between the legs created. For each of several cases tested with changing jet-ejecting conditions, no difference is found in the importance of the role of the hairpin structure. Therefore, we conclude that the hairpin vortex with widespread legs is a key structure in the transition to turbulence.

本文言語English
論文番号013904
ジャーナルPhysical Review Fluids
3
1
DOI
出版ステータスPublished - 2018 1

ASJC Scopus subject areas

  • 計算力学
  • モデリングとシミュレーション
  • 流体および伝熱

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