This study demonstrates the feasibility of characterizing small-scale flow dynamics using path-specific Particle Residence Time (PRT). PRT, defined as the time a parcel of fluid spends in a region of interest, is a clear indicator of stagnation and recirculation. To test the concept, two-dimensional particle tracking velocimetry is used to measure a laminar separation bubble (LSB) on the suction side of an SD7003 airfoil at $$Re=60,000$$ . Extended pathlines are calculated from the Lagrangian data such that fluid parcels entering the region of interest are tracked continuously. PRT is then directly calculated and used to quantify the entrainment process across the LSB. Using convential Eulerian quantities, the flow field around the LSB is divided into outer (free stream) and inner layers—separated by the local minimum velocity magnitude line. Entrainment, initiated by the formation of vortices near the reattachment point, is quantified according to the trajectories of fluid parcels crossing into the inner flow layer. The PRT values of entrained fluid parcels are significantly increased compared to the bulk flow. Variations of the mean PRT of entrained fluid reveal unsteady features, including the transition and reattachment of the LSB. The path-dependent indicators of separation, transition and reattachment are shown to closely agree with Eulerian-based benchmark measurements.

中文翻译：

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使用粒子停留时间表征夹带动力学的直接拉格朗日方法：层流分离气泡的案例研究

这项研究证明了使用特定路径的粒子停留时间 (PRT) 来表征小尺度流动动力学的可行性。PRT，定义为流体在感兴趣区域停留的时间，是停滞和再循环的明确指标。为了测试这个概念，二维粒子跟踪测速仪用于测量 SD7003 翼型吸力侧的层流分离气泡 (LSB)，$Re=60,000$$。根据拉格朗日数据计算扩展路径，以便连续跟踪进入感兴趣区域的流体包裹。然后直接计算 PRT 并用于量化整个 LSB 的夹带过程。使用常规欧拉量，LSB 周围的流场分为外层（自由流）和内层——由局部最小速度大小线分隔。由重新附着点附近的涡流形成引发的夹带根据穿过内部流动层的流体包裹的轨迹进行量化。与整体流相比，夹带流体包的 PRT 值显着增加。夹带液体的平均 PRT 的变化揭示了不稳定的特征，包括 LSB 的过渡和重新附着。分离、过渡和重新附着的路径依赖指标与基于欧拉的基准测量非常一致。夹带液体的平均 PRT 的变化揭示了不稳定的特征，包括 LSB 的过渡和重新附着。分离、过渡和重新附着的路径依赖指标与基于欧拉的基准测量非常一致。夹带液体的平均 PRT 的变化揭示了不稳定的特征，包括 LSB 的过渡和重新附着。分离、过渡和重新附着的路径依赖指标与基于欧拉的基准测量非常一致。