Shear layers driven by turbulent plumes
Shear layers driven by turbulent plumes
复制标题
由湍流羽流驱动的剪切层
DOI：
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发表时间：
2001
影响因子：
3.7
通讯作者：
G. Hughes
中科院分区：
文献类型：
--
作者：
A. Wong;R. W. Griffiths;G. Hughes
一个湍流羽流从一个连续源的浮力在一个长的坦克被示出产生一系列的准稳定的逆流水平剪切层整个坦克。水平流速和剪切层的深度都随着羽流流出上方/下方距离的增加而减小。剪切层由羽流产生的稳定密度分层支撑，并叠加在垂直平流和夹带流入上，构成所谓的“填充箱”环流。因此，在某些深度，周围的水从羽流中流走，而不是被夹带，尽管我们没有看到密集羽流水的“疏散”证据。考虑到羽流在很长时间内产生的分层，速度结构调整到强迫变化的时间尺度与长的内部重力波在水槽长度上传播的时间成比例。剪切层解释的内部正常模式，激发，并反过来确定，水平羽流流出。第六和第七斜压模态通常占主导地位，因为在羽流流出的水平上，它们的相速度近似等于“填充盒”中的垂直平流，并且与之相反。此外，相速度和平流之间的近似平衡被发现持有整个坦克，导致在观察到的准稳态流结构。粘度导致剪切层中的水平速度随羽流流出上方/下方的距离而减小，并且被认为是实验期间观察到的流动结构中的低频振荡的原因。
A turbulent plume from a continuous source of buoyancy in a long tank is shown to generate a series of quasi-steady counterflowing horizontal shear layers throughout the tank. Both the horizontal flow velocity and the depth of the shear layers are observed to decrease with distance above/below the plume outflow. The shear layers are supported by the stable density stratification produced by the plume and are superimposed on the vertical advection and entrainment inflow that make up the so-called ‘filling box’ circulation. Thus, at some depths, the surrounding water flows away from the plume instead of being entrained, although we see no evidence of ‘detrainment’ of dense plume water. Given the stratification produced by the plume at large times, the timescale for the velocity structure to adjust to changes in forcing is proportional to the time for long internal gravity waves to travel the length of the tank. The shear layers are interpreted in terms of internal normal modes that are excited by, and which in turn determine, the horizontal plume outflow. The sixth and seventh baroclinic modes typically dominate because at the level of the plume outflow their phase speed is approximately equal and opposite to the vertical advection in the ‘filling box’. Also, the approximate balance between phase speed and advection is found to hold throughout the tank, resulting in the observed quasi-steady flow structure. Viscosity causes the horizontal velocity in the shear layers to decrease with distance above/below the plume outflow, and is thought to be responsible for a low-frequency oscillation in the flow structure that is observed during experiments.