In the present study, the sudden changes of the flow field past stalled airfoils for small variations of the Reynolds number are investigated numerically. A vortex particle method has been used for the simulations in a two-dimensional framework. The most critical configurations found with this solver are verified through the comparison with the solution given by a mesh-based finite volume solver. The airfoils considered are the NACA0010 and a narrow ellipse with the same thickness. The angle of attack is fixed to $\unicode[STIX]{x1D6FC}=30^{\circ }$ for which complex dynamics of the flow can take place in the different viscous regimes inspected. The Reynolds number ranges between $Re=100$ and $Re=3000$ and, within this interval, numerous bifurcations of the solution are observed in terms of mean lift and drag coefficients, Strouhal number and downstream wake. An analysis of these bifurcations is provided and links are made between the wake structures observed. On this base the flow patterns can be classified in different modes similarly to the analysis by Kurtulus (Intl J. Micro Air Vehicles, vol. 7(3), 2015, pp. 301–326; vol. 8(2), 2016, pp. 109–139). A discussion of the vortical evolution of the flow in the vicinity of the suction side of the airfoil is also provided.

中文翻译：

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改变雷诺数时，失速翼型上的流动多次分叉

在本研究中，对雷诺数的微小变化导致失速翼型流场的突然变化进行了数值研究。涡旋粒子法已用于二维框架中的模拟。通过与基于网格的有限体积求解器给出的解决方案进行比较，验证了使用该求解器找到的最关键配置。考虑的翼型是 NACA0010 和具有相同厚度的窄椭圆。攻角固定为$\unicode[STIX]{x1D6FC}=30^{\circ }$在所检查的不同粘性状态下，可能会发生复杂的流动动力学。雷诺数介于$重新=100$和$重新=3000$并且，在这个区间内，在平均升力和阻力系数、斯特劳哈尔数和下游尾流方面观察到解的许多分岔。提供了对这些分叉的分析，并在观察到的尾流结构之间建立了联系。在此基础上，流型可以分为不同的模式，类似于 Kurtulus 的分析（国际 J. 微型飞行器, 卷。7(3)，2015，第 301-326 页；卷。8(2)，2016，第 109-139 页）。还提供了对翼型吸力侧附近流动的涡旋演化的讨论。