We investigate the behavior of large particles in a transitional swirling flow in a closed vessel, focusing on both their transport and flow sampling. We conduct a Lagrangian study of slightly buoyant particles, considering three particle diameters, keeping the fluid's density and velocity magnitude constant and varying the Reynolds number by changes of the fluid's viscosity. The literature lacks study of material particles in such flows, where chaos and bursts of turbulence can exist, despite applications in industrial and natural situations. One striking result is that particles beyond a certain size, between 10 and 18 mm, are subject to a strong trapping in the vicinity of the islands of the laminar flow, while large particles below this threshold sample the flow homogeneously, independently of the Reynolds number. The exploration of the flow by the large particles is widely different from the preferential sampling in fully developed turbulent conditions, in terms of characteristic times associated with motions escaping the regions and dimensions of the sampled regions. While the particle mean velocity is found to be independent of both the fluid's viscosity and particle size, the fluctuation magnitude strongly increases with decreasing flow viscosity and is marginally affected by size. We also characterize the intensity of the trapping through probability density functions of the particle positions, a measure of the dimensions of the sampled regions, and particle position autocorrelation functions as an attempt to quantify residence times. A qualitative origin for the trapping existence criterion based on a shear-induced lift force is proposed, as an argument for its sole dependence on particle size.

中文翻译：

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大颗粒通过涡流的湍流过渡而传输

我们研究了密闭容器中过渡涡旋流中大颗粒的行为，重点研究了它们的运输和流量采样。我们对微浮力颗粒进行了拉格朗日研究，考虑了三个粒径，保持流体的密度和速度大小不变，并通过改变流体的粘度来改变雷诺数。尽管在工业和自然环境中有应用，但文献中仍缺乏对此类流体中可能存在混沌和湍流爆发的物质颗粒的研究。一个惊人的结果是，超过一定大小（在10到18毫米之间）的粒子在层流岛附近受到强烈的捕获，而低于此阈值的大粒子则独立地对流量进行采样，而与雷诺数无关。大颗粒对流的探测与充分发展的湍流条件下的优先采样有很大的不同，就其与运动相关的特征时间而言，它们逃离了采样区域的区域和尺寸。虽然发现颗粒平均速度与流体的粘度和颗粒大小均无关，但波动幅度会随着流动粘度的降低而大大增加，并且受尺寸的影响很小。我们还通过粒子位置的概率密度函数，采样区域尺寸的度量以及粒子位置自相关函数来表征捕获强度，以此来尝试量化停留时间。提出了基于剪力的提升力的圈闭存在准则的定性来源，