Three dimensional flows beneath a thin layer of 2D turbulence induced by Faraday waves
Three dimensional flows beneath a thin layer of 2D turbulence induced by Faraday waves
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DOI：
10.1007/s00348-020-03099-y
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发表时间：
2021-01-01
影响因子：
2.4
通讯作者：
von Kameke, Alexandra
中科院分区：
文献类型：
--
作者：
Colombi, Raffaele;Schlueter, Michael;von Kameke, Alexandra
法拉第波发生在受到垂直振动的流体上。虽然众所周知，波形的形式和形状取决于驱动振幅和频率，但直到最近的研究才发现在表面存在水平速度场，称为法拉第流。这种流动表现出二维湍流的属性，并在这项研究中被复制。尽管人们越来越关注法拉第流和其他非严格二维（2D）系统中的逆能通量，但对流体表面下的速度场却知之甚少。本文利用高时空分辨率的粒子图像测速技术测量了水面及水面以下不同深度的平面速度场，在水面以下半个法拉第波长处观察到速度和湍动能的突然下降，揭示了水面流是湍流运动的主要来源。表面下的流动结构包括比表面上的那些更大的空间尺度，导致非常长尾的时间和空间速度（自）相关函数。的三维流动的可压缩性，这增加了强烈的深度，而分歧改变其外观从间歇性和单一的事件，一个大规模的模式，类似于2D切割平面的对流卷。我们的研究结果表明，表面下的整体流体流动是高度三维的，并且反向级联和受限的二维湍流可以与三维流动共存。图形摘要
Faraday waves occur on a fluid being subject to vertical shaking. Although it is well known that form and shape of the wave pattern depend on driving amplitude and frequency, only recent studies discovered the existence of a horizontal velocity field at the surface, called Faraday flow. This flow exhibits attributes of two-dimensional turbulence and is replicated in this study. Despite the increasing attention towards the inverse energy flux in the Faraday flow and other not strictly two-dimensional (2D) systems, little is known about the velocity fields developing beneath the fluid surface. In this study, planar velocity fields are measured by means of particle image velocimetry with high spatio-temporal resolution on the water surface and at different depths below it. A sudden drop in velocity and turbulent kinetic energy is observed at half a Faraday wavelength below the surface revealing that the surface flow is the main source of turbulent fluid motion. The flow structures below the surface comprise much larger spatial scales than those on the surface leading to very long-tailed temporal and spatial velocity (auto-) correlation functions. The three-dimensionality of the flow is estimated by the compressibility, which increases strongly with depth while the divergence changes its appearance from intermittent and single events to a large scale pattern resembling 2D cut-planes of convection rolls. Our findings demonstrate that the overall fluid flow beneath the surface is highly three-dimensional and that an inverse cascade and aspects of a confined 2D turbulence can coexist with a three-dimensional flow.Graphic abstract