风维持粘性孤子
Wind-sustained viscous solitons
摘要：
当风吹在足够高粘度的液体表面时，首先产生小振幅的波包，其零星地形成快速向下游传播的大振幅流体隆起。这些非线性结构首先由Francis [Philos.Mag.42，695（1954）]观察到，它们有一个几乎垂直的迎风后部和一个弱倾斜的前部。我们称之为粘性孤子。我们在风洞实验中使用运动粘度为1000 mm ^2 s^-1的硅油，通过激光片层轮廓测量和粒子图像速度测量研究了它们的动力学。我们给他们的亚临界性质的证据：他们是在一个地区发出的大剪切应力，但一旦形成，他们是持续的风和传播在一个地区的应力较低。它们的传播速度由空气中的气动阻力和液体中的粘性阻力之间的平衡给出。根据在不同风速和沿通道距离下测得的孤子振幅，重建了亚临界分岔图的稳定孤子分支。当风速较大时，孤子的发射频率增加，导致新形成的上游孤子对下游成熟孤子的长距离遮蔽，从而限制了它们的传播。
英文摘要：
When wind blows at the surface of a liquid of sufficiently high viscosity, a wave packet of small amplitude is first generated, which sporadically forms large-amplitude fluid bumps that rapidly propagate downstream. These nonlinear structures, first observed by Francis [Philos. Mag. 42, 695 (1954)], have an almost vertical rear facing the wind and a weak slope at the front. We call them viscous solitons. We investigate their dynamics in a wind-tunnel experiment using silicon oil of kinematic viscosity 1000 mm^2 s^-1 by means of laser sheet profilometry and particle image velocimetry. We give evidence of their subcritical nature: they are emitted in a region of large shear stress but, once formed, they are sustained by the wind and propagate in a region of lower stress. Their propagation velocity is given by the balance between aerodynamic drag in the air and viscous drag in the liquid. The stable soliton branch of the subcritical bifurcation diagram is reconstructed from the measured soliton amplitude at various wind velocities and distances along the channel. At large wind velocity, the emission frequency of solitons increases, resulting in a long-range sheltering of downstream mature solitons by newly formed upstream solitons, which limits their course.
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