Fractal, classical, and active grid turbulence: From production to decay
Fractal, classical, and active grid turbulence: From production to decay
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分形、经典和主动网格湍流：从产生到衰变
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发表时间：
2015
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通讯作者：
R. J. Hearst
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作者：
R. J. Hearst
分形、经典和活动网格湍流：从产生到衰变罗伯特·杰森·赫斯特博士，多伦多大学航空航天研究所研究生系2015年在分形网格之后产生的湍流已被证明表现出特殊的衰减特性，这与对典型网格湍流流动的预期相反。这种流动被称为“非平衡”湍流，其特点是湍流动能的衰减率和归一化耗散率相对于正则网格湍流的快速增长。因此，这项工作的主要目的是通过一系列使用热线风速仪的风洞实验来协调现代分形生成的网格湍流和正则网格湍流。将正方形分形元网格产生的湍流与两个规则正方形网格和一个活动网格产生的湍流进行了比较。三个被动网格都有相同的阻塞，而主动网格的阻塞是暂时的。规则网格和活动网格被用作比较的基准，因为它们产生的准平衡湍流符合Richardson-Kolmogorov平衡湍流现象学的许多预测，除了惯性范围内k−5/3谱的存在。结果表明，非平衡湍流和准平衡湍流是湍流生成网格下游同一湍流演化的两个阶段。流动从靠近网格的非平衡湍流开始，向下游演化为准平衡湍流。这一发现的证据表明，在离分形几何足够远的地方，流动返回到准平衡状态，具有传统的衰减率和恒定的归一化耗散标度。经研究发现，
Fractal, Classical, and Active Grid Turbulence: From Production to Decay Robert Jason Hearst Doctor of Philosophy Graduate Department of the Institute for Aerospace Studies University of Toronto 2015 The turbulence produced in the wake of fractal grids has been shown to exhibit peculiar decay properties that contrast with expectations for canonical grid turbulence flows. Such flows have been termed ‘non-equilibrium’ turbulence, and feature an unexpectedly high decay rate of turbulent kinetic energy and rapid growth of the normalized dissipation rate relative to canonical grid turbulence flows. The primary aim of this work is thus to reconcile modern fractal-generated grid turbulence with canonical grid turbulence via a series of wind tunnel experiments using hot-wire anemometry. The turbulence produced by a square-fractal-element grid, that is known to generate a significant non-equilibrium region in its wake, is compared to the turbulence produced by two regular square mesh grids and an active grid. The three passive grids all have the same blockage, while the blockage of the active grid is transient. The regular grids and active grid are used as benchmarks for comparison because they are known to produce quasi-equilibrium turbulence that matches many of the predictions of Richardson-Kolmogorov equilibrium turbulence phenomenology, save the existence of a k−5/3 spectrum in the inertial range. It is found that non-equilibrium and quasi-equilibrium turbulence are two phases of the same turbulence evolution downstream of turbulence generating grids. The flow begins as non-equilibrium turbulence close to the grid, and evolves downstream into quasiequilibrium turbulence. Evidence for this finding is provided by showing that sufficiently far downstream of the fractal geometry the flow returns to a quasi-equilibrium state with traditional decay rates and constant normalized dissipation scaling. It is found that the
湍流中脉动速度和标量梯度的实验估计
影响因子：
2.4
作者：
Hearst R
通讯作者：
Hearst R