Multiple stages of decay in two-dimensional turbulence
Multiple stages of decay in two-dimensional turbulence
复制标题
二维湍流中的多个衰变阶段
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
N. Ouellette
中科院分区：
文献类型：
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作者：
L. Fang;N. Ouellette
我们报告了准二维实验室流中湍流自由衰减的测量结果。我们观察到三个明显不同的衰变阶段，每个阶段的特征是动能随时间呈指数下降，但具有不同的衰变常数。使用过滤技术，我们确定了控制每个衰变阶段的物理原理。第一个也是最快速的阶段并不是像人们经常认为的那样是由于同号涡旋的合并，而是由于小尺度光谱能量泄漏的快速松弛。第二阶段是动态逆能量级联过程的表现，一直持续到尺度分离变小。在我们的实验中，衰变的最后阶段似乎由垂直分层主导。我们的结果阐明了二维湍流衰减中的动力学过程。
We report measurements of the free decay of turbulence in a quasi-two-dimensional laboratory flow. We observe three clearly distinguished stages of decay, each characterized by an exponential decrease of the kinetic energy with time, but with different decay constants. Using filtering techniques, we identify the physics that controls each stage of decay. The first and most rapid stage is not due to the merger of like-sign vortices as has often been suggested but rather to the rapid relaxation of downscale spectral energy leakage. The second stage is a manifestation of dynamical inverse energy cascade processes and lasts until the separation of scales becomes small. The final stage of decay appears to be dominated by the vertical stratification in our experiment. Our results clarify the dynamical processes at work in decaying two-dimensional turbulence.