Experiments on a turbulent plume: Shape analyses
Experiments on a turbulent plume: Shape analyses
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DOI：
10.1029/2010jb007633
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发表时间：
2011-03-30
影响因子：
3.9
通讯作者：
Sumita, Ikuro
中科院分区：
文献类型：
--
作者：
Kitamura, Shogo;Sumita, Ikuro
我们报告的实验室实验结果的湍流羽流，一个简化的模型，积极浮力火山羽流与一个小的内容的细灰研究羽流的形状如何变化的函数的时间。为了模拟这样的羽流，我们不断地注入一个稠密的流体在一个恒定的出口速度向下，并研究如何羽流形状随时间的变化，涡流发展从流动不稳定性和夹带。本文以出口速度和密度差为变参数进行了一系列实验，在实验室实现了射流-羽流的转捩。最初的羽流有一个“手指状”的形状，变得不稳定，并形成一个“羽流头”，后来转化为一个“圆锥状”的自相似形状。我们还发现，当浮力变得足够大的惯性相比，有一个暂时的偏离锥状形状，形成一个“头锥。“我们设计了新的方法来定量描述这些形状的变化，并定义了四个政权作为时间的函数。我们发现，流动不稳定性和政权的发病时间有负幂律依赖于初始雷诺数（或出口速度），浮力导致政权转变变得更早。我们的实验表明，监测上升的火山羽流的形状的变化和分析制度的开始时间，可以用来作为一种措施，以限制他们的浮力。
We report the results of laboratory experiments on a turbulent plume, a simplified model of a positively buoyant volcanic plume with a small content of fine ash to study how the shape of the plume changes as a function of time. To model such plumes, we continuously inject a dense fluid downward at a constant exit velocity and study how the plume shape changes with time as vortices develop from flow instability and entrainment. Here a series of experiments are conducted with exit velocity and the density difference as the changeable parameters, and the jet-plume transition is realized in the laboratory. Initially the plume has a "finger-like" shape which becomes unstable and forms a "plume head" and later transforms into a "cone-like" self-similar shape. We also find that when the buoyancy becomes sufficiently large compared to inertia, there is a temporary deviation from the cone-like shape to form a "headed cone." We devise new methods to quantitatively characterize these changes of shape and define four regimes as a function of time. We find that the onset times of the flow instability and the regimes have negative power law dependence on the initial Re (or the exit velocity), and that buoyancy causes the regime transitions to become earlier. Our experiments suggest that monitoring the change of the shape of the rising volcanic plumes and analyzing the regime onset times, can be used as a measure to constrain their buoyancy.