As a fundamental phenomenon of fluid mechanics, recent studies suggested laminar-turbulent transition belonging to the universality class of directed percolation. Here, the onset of a laminar separation bubble on an airfoil is analyzed in terms of the directed percolation model using particle image velocimetry data. Our findings indicate a clear significance of percolation models in a general flow situation beyond fundamental ones. We show that our results are robust against fluctuations of the parameter, namely, the threshold of turbulence intensity, that maps velocimetry data into binary cells (turbulent or laminar). In particular, this percolation approach enables the precise determination of the transition point of the laminar separation bubble, an important problem in aerodynamics.

中文翻译：

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空气动力学和渗流：翼型上展开的层流分离气泡

作为流体力学的基本现象，最近的研究表明层流湍流跃迁属于定向渗流的普遍性类别。在此，使用粒子图像测速数据根据定向渗流模型对翼型上的层状分离气泡的发生进行了分析。我们的发现表明，渗流模型在基本模型以外的一般流动情况下具有明显的意义。我们表明，我们的结果对参数波动即湍流强度阈值具有鲁棒性，该参数将测速数据映射到二元单元（湍流或层流）中。尤其是，这种渗流方法能够精确确定层流分离气泡的过渡点，这是空气动力学中的一个重要问题。