We show that 2D Navier–Stokes and Euler flows with localised vorticity always feature regular structures in the far field. The level lines of each component of the velocity, at large distances, tend to have the symmetries of a regular polygon: a digon if the total circulation is non-zero; a square for flows with zero total circulation and non-integrable velocity; an hexagon for flows with integrable velocity and, exceptionally, a polygon with more than six sides.

中文翻译：

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具有局部涡度的二维流的远场几何结构

我们证明了具有局部涡度的二维Navier–Stokes和Euler流在远场中始终具有规则的结构。速度的每个分量的水平线在很远的距离处往往具有正多边形的对称性：如果总循环量不为零，则为对角线；否则，为正多边形。总流量为零且不可积速度为零的正方形; 一个六角形，用于以不可积分的速度流动，另外，一个多边形具有六个以上的边。