卡门涡街 【图，力有方向】

因为在卡门涡街里游泳特别省力，虹鳟还会主动寻找卡门涡街，比如流水中的大石头后面。垂钓的人都知道，鳟鱼喜欢躲在石头后面“歇脚”，这个现象背后就是这个道理。

High Intermediate Reynold’s Numbers (50–200,000): With still larger objects or higher relative velocities, the generated vortices become very large and are “shed” into the downstream fluid. Instead of two attached vortices at any time, a single vortex forms downstream from the separation point on one side of the object until it is shed, and then a second vortex forms with the opposite circulation pattern behind the opposite separation point. The two sides of the object thus alternate in creating shed vortices. The result is two parallel trails of downstream vortices called a von Kármán vortex street:

高中间雷诺数(50–200，000):对于更大的物体或更高的相对速度，产生的涡流变得非常大，并“脱落”到下游流体中。不是在任何时候都有两个附着的旋涡，而是在物体一侧的分离点下游形成单个旋涡，直到脱落，然后在相反的分离点后面形成具有相反环流模式的第二个旋涡。因此，物体的两侧交替产生脱落涡流。其结果是下游涡旋的两条平行轨迹，称为冯·卡门涡街: