论文标题
雷诺数很高的湍流的极端耗散和间歇性
Extreme dissipation and intermittency in turbulence at very high Reynolds numbers
论文作者
论文摘要
湍流中极端的耗散事件很少见，但它们的数量级可能比平均耗散率强。尽管它在许多小规模的物理过程中的重要性，但目前尚无准确的理论或模型来预测极值是雷诺数的函数。在这里，我们根据重要的剪切层的概念引入了耗散PDF的新模型，该模型是局部平均耗散升高的薄区域。在很高的雷诺数中，这些重要的剪切层会产生分层的子结构。流量域分为不同的层区域和背景区域，每个区域都有自己的耗散pdf。将体积加权区域PDF组合在一起以获得整体PDF，随后用于确定耗散差异和最大值。该模型可为耗散最大和方差的雷诺数量表产生与可用数据一致的范围。此外，发现功率定律缩放指数随雷诺数逐渐增加，这也与数据一致。表明，增加的指数对大气和天体物理雷诺数的湍流具有深远的影响。目前的结果强烈表明，间歇性的显着剪切层结构是理解和量化极端耗散的关键，更一般而言是极端速度梯度。
Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation PDF based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds number, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.
