AI 中文总结
该研究通过DNS、POD和网络基序分析，揭示了不同雷诺数构型下近壁湍流的偏好动力学路径，外层活动可改变其出现概率。
AI 中文摘要
我们通过将相干结构能量表示为低维状态空间中的轨迹，并利用网络基序分析重复出现的轨迹模式，来识别壁面受限湍流近壁区域的动力学过程。针对三种构型开展了直接数值模拟（DNS）：雷诺数 $Re_\tau \approx 180$ 的最小流动单元（MFU），用于分离自维持过程（SSP）；相同雷诺数下的全尺寸通道，用于研究近壁结构间的相互作用；$Re_\tau \approx 2200$ 的MFU，用于探究近壁区与外层的耦合。采用本征正交分解（POD）识别对应SSP的条纹、 rolls（涡卷）及蜿蜒结构的模态，并将流动投影至这些模态以跟踪其能量随时间的变化。随后通过基序分析在所得状态空间轨迹中识别出具有统计显著性的动力学路径。多个基序在三种构型中均存在，表明不同背景流动下近壁动力学具有鲁棒性；虽可识别出与经典SSP相关的基序，但也存在同等显著、无直接SSP对应物的基序，说明近壁的偏好动力学超出了经典的再生循环。对 $Re_\tau \approx 180$ 的MFU以外层能量为条件进一步显示：平静的外层状态产生的动力学类似低雷诺数全通道的情况，而活跃的外层状态则促进高能量的猝发事件。这些结果表明，近壁湍流沿偏好的动力学路径演化，外层活动可改变这些路径的出现概率，但无法将其消除。
英文摘要
We identify dynamical processes in the near-wall region of turbulent wall-bounded flow by representing coherent-structure energy as trajectories in a low-dimensional state space and analyzing recurring trajectory patterns using network motifs. Direct numerical simulations (DNS) are performed for three configurations: a minimal flow unit (MFU) at $Re_τ\approx 180$ to isolate the self-sustaining process (SSP), a full-scale channel at the same Reynolds number to study interactions between near-wall structures, and an MFU at $Re_τ\approx 2200$ to investigate near-wall/outer-layer coupling. Proper orthogonal decomposition (POD) is used to identify modes corresponding to streaks, rolls, and meandering structures of the SSP, and the flow is projected onto these modes to track their energy over time. Motif analysis then identifies statistically significant dynamical pathways in the resulting state-space trajectories. Several motifs are common to all three configurations, indicating robust near-wall dynamics across different background flows. While motifs associated with the classical SSP are recovered, equally prominent motifs with no direct SSP analogue are also identified, demonstrating that preferred near-wall dynamics extend beyond the canonical regeneration cycle. Conditioning the $Re_τ\approx 180$ MFU on outer-layer energy further shows that quiescent outer-layer states produce dynamics resembling those of the low-Reynolds-number full channel, whereas energetic outer-layer states promote high-energy bursting events. These results demonstrate that near-wall turbulence evolves along preferred dynamical pathways whose prevalence is modified, but not eliminated, by outer-layer activity.
Comments32 pages, 18 figures. Under consideration for publication in J. Fluid Mech
