In this Letter, the velocity structures and the extension behavior of localized turbulent bands in channel flows are measured by particle image velocimetry in a plane parallel to the walls and are analyzed by comparing with direct numerical simulations at low Reynolds numbers. It is illustrated that the convection velocity of the band head (band’s downstream end) is not determined by the formation and propagation of low-speed streaks but by a high-speed “hat” shaped region near the band head. This “hat” region travels downstream obliquely like a solitary wave and leaves newly generated low-speed streaks to travel slowly in the spanwise direction, leading to the head extension of turbulent bands.

中文翻译：

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通道中湍流带下游端的延伸

在这封信中，在平行于壁的平面上通过粒子图像测速法测量了通道流动中局部湍流带的速度结构和扩展行为，并通过与低雷诺数下的直接数值模拟进行了比较进行了分析。可以看出，带头（带的下游端）的对流速度不是由低速条纹的形成和传播决定的，而是由带头附近的高速“帽”形区域决定的。该“帽子”区域像孤波一样向下游倾斜传播，并且使新生成的低速条纹沿翼展方向缓慢传播，从而导致湍流带的头部延伸。