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アクティブネマティック乱流への不連続遷移

Malcolm Hillebrand1,2,3, Ricard Alert4,5,6,7,8,9

  • 1Max Planck Institute for the Physics of Complex Systems, Dresden, Germany.

Nature communications
|December 15, 2025
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まとめ

アクティブ流体におけるアクティブ乱流への遷移は不連続であり、速度の突然のジャンプと、層流およびカオス的流れ状態間の二安定性が特徴である。これは、閉じ込められた系で観察される連続的な遷移とは対照的である。

キーワード:
アクティブ流体アクティブネマティクスアクティブ乱流不連続遷移二安定性ヒステリシス流体力学ソフトマター物理学

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科学分野:

  • 物理学
  • 流体力学
  • ソフトマター物理学

背景:

  • アクティブ流体は、低いレイノルズ数でカオス的な流れを示し、アクティブ乱流と呼ばれる。
  • アクティブ乱流の統計的性質は理解されているが、層流から乱流への遷移は不明なままである。

研究 の 目的:

  • 非制限系、欠陥のないアクティブネマティクスにおける層流から乱流への遷移を調査する。
  • この遷移の性質、すなわち連続的か不連続的かを特徴づける。

主な方法:

  • アクティブネマティクスの最小モデルのシミュレーション。
  • 二乗平均速度、二安定性、ヒステリシス、および有限時間リアプノフ指数の解析。

主要な成果:

  • アクティブ乱流への遷移は不連続であり、二乗平均速度のジャンプによって特徴づけられる。
  • 層流とカオス的流れの間の二安定性とヒステリシスが観察された。
  • 遷移のための臨界アクティビティ数（A* ≈ 4900）が特定された。
  • 遷移を下回る振動および長いカオス的遷移につながる亜臨界分岐が発生する。

結論:

  • 非制限系アクティブネマティクスにおけるアクティブ乱流への遷移は不連続である。
  • ストークス流における長距離流体力学的相互作用は、流れ状態の空間的共存を抑制し、不連続遷移につながる可能性が高い。
  • この結果は、閉じ込められた系における連続的な遷移とは対照的である。