Aeration Due to Breaking Waves
Aeration Due to Breaking Waves
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DOI：
10.14264/uql.2015.70
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Peter D. Cummings
中科院分区：
文献类型：
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作者：
Peter D. Cummings
海洋和大气之间的物质交换(气体、水和盐)对维持地球上的生命至关重要。在高风速时，这种交换主要归因于破碎的波浪夹带气泡。采用垂直支承的平面下沉射流实验对卷吸过程进行了模拟。用双尖端电导探头和摄像机检测气泡。当俯冲射流速度低于1.0m/S时，没有气泡夹带。对于大型粗糙湍动射流，这一初始速度似乎有一个弗劳德和韦伯数标度。在射流速度高达5m/S的情况下，气流似乎是通过射流-俯冲池交汇处的间歇性气腔被卷吸的。卷吸空气包随后在卷吸点下的两相自由剪切层中破裂。在较高的射流速度下，在撞击前，充气射流表面可能通过脉动感应腔的部分穿透，以及射流自曝气的卷吸。俯冲射流气流数据显示了不同类型的卷吸机制。单相扩散模型能较好地描述剪切层发育带。气泡的扩散过程近似为高斯自相似过程。平均气泡速度分布可以用Goertler误差函数或双曲正切模型来模拟。在一定的喷流速度范围内，气泡谱近似为对数正态分布，几何平均直径为1.0-2.0 mm。发现气泡韦伯数可以模拟直径约为10 mm的最大气泡尺寸。对涡片势流解的一个原始修正是一个简单且相当精确的水面重力波有限振幅模型，特别是在深水中。该模型具有一些有趣的特点，如垂直和水平不对称和驻波水面模拟。本文介绍了一个简单而有见地的海面风浪发展模型，该模型采用一个固定的海面雷诺数U*·Sqrt(Lf)/GAMA，其中U*=风摩擦速度，L=波长，F=FETCH，GAMMA=每个波长的波场涡旋环流。所得结果可用于海-气交换的模拟、预报结构物上的破碎波浪力，以及在工业上使用平面下沉射流作为曝气装置。
The exchange of mass (gases, water & salts) between the oceans and the atmosphere is vital to the maintenance of life on earth. At high wind velocities most of this exchange is attributable to breaking wave entrained air bubbles. A vertical supported planar plunging jet experiment was used to model the entrainment process. The bubbles were detected with a dual tip conductivity probe and a video camera. At plunging jet velocities below 1.0m/s there is no bubble entrainment. This inception velocity appears to have a Froude and Weber number scaling for large rough turbulent jets. At jet velocities up to 5m/s air appeared to be entrained via intermittent air cavities at the jet - plunge pool intersection. The entrained air packets subsequently break in the two phase free shear layer under the entrainment point. At higher jet velocities there may be partial penetration of the aerated jet surface via pulsating induction cavities plus air entrainment via jet self aeration before impact. Plunging jet air flow data displays the different types of entrainment mechanisms. Mono-phase diffusion models can be successfully adapted to describe the shear layer developing zone. The diffusion of the air bubbles is approximately a Gaussian self similar process. The mean bubble velocity profiles can be modelled using the Goertler Error function or Hyperbolic Tangent models. The bubble spectra is approximately Lognormal with a geometric mean diameter of 1.0-2.0mm for a range of jet velocities. A bubble Weber number is found to model the maximum bubble size of approximately 10mm diameter. An original adaptation of the potential flow solution for the vortex sheet is shown to be a simple and reasonably accurate finite amplitude model for water surface gravity waves, especially in deep water. This model has some interesting features, such as both vertical and horizontal asymmetry and standing wave water profile modelling. A simple and possibly insightful model of wave growth due to the wind is introduced, using a constant sea surface Reynolds number U*.sqrt(LF)/Gamma, where U* = wind friction velocity, L = wavelength, F = fetch, and Gamma = wave field vortex circulation per wavelength. The results may have application in the modelling of air - sea gas exchanges, predicting breaking wave forces on structures and the use of the planar plunging jet as an aeration device in industry.