标题： 小尺度各向异性由谱强迫和旋转在非螺旋和螺旋湍流中引起 显示英文标题

标题： Small-scale anisotropy induced by spectral forcing and by rotation in non-helical and helical turbulence

摘要： 我们研究了大尺度光谱强迫对均匀不可压缩湍流直接数值模拟中速度场尺度相关各向异性的影响。 考虑了两种强迫方法：稳态ABC单波数方案和非定常无螺旋或螺旋欧拉方案。 结果还与通过负粘性方案获得的高分辨率数据进行了比较。 使用了一种细粒度的各向异性表征，即测量与两点速度相关性相关的某些量：我们对谱速度张量进行了模态分解，得到能量、螺旋度和极化谱。 此外，我们还包括了这三个谱对波矢方向的显式依赖。 明确识别了由于强迫本身导致小尺度各向异性发展的条件。 结果显示，在预期为各向同性的湍流中，ABC强迫在最小解析尺度上产生显著的能量和螺旋度方向各向异性，就像在使用不利强迫尺度时的螺旋欧拉方案一样。 然后在旋转湍流中研究了方向和尺度相关的各向异性。 首先表明，在ABC强迫的模拟中，能量谱的斜率发生了变化，各向异性水平类似于欧拉强迫运行中较低罗斯比数下的水平，这一结果既由于强迫本身的性质，也由于它允许反向级联的发展。 其次，我们表明，即使在低旋转速率下，科里奥利力引起的自然各向异性在所有尺度上都是可见的。 最后，我们确定了两个不同的波数范围，在这些范围内各向异性行为不同，并且如果罗斯比数不是太低，区分它们的特征长度尺度是旋转和耗散效应平衡的尺度。 显示英文摘要

摘要： We study the effect of large-scale spectral forcing on the scale-dependent anisotropy of the velocity field in direct numerical simulations of homogeneous incompressible turbulence. Two forcing methods are considered: the steady ABC single wavenumber scheme and the unsteady non-helical or helical Euler scheme. The results are also compared with high resolution data obtained with the negative viscosity scheme. A fine-grained characterization of anisotropy, consisting in measuring some quantities related to the two-point velocity correlations, is used: we perform a modal decomposition of the spectral velocity tensor into energy, helicity and polarization spectra. Moreover, we include the explicit dependence of these three spectra on the wavevector direction. The conditions that allow anisotropy to develop in the small scales due to forcing alone are clearly identified. It is shown that, in turbulent flows expected to be isotropic, the ABC forcing yields significant energy and helicity directional anisotropy down to the smallest resolved scales, like the helical Euler scheme when an unfavourable forcing scale is used. The direction-and scale-dependent anisotropy is then studied in rotating turbulence. It is first shown that, in the ABC-forced simulations the slope of the energy spectrum is altered and the level of anisotropy is similar to that obtained at lower Rossby number in Euler-forced runs, a result due both to the nature of the forcing itself and to the fact that it allows an inverse cascade to develop. Second, we show that, even at low rotation rate, the natural anisotropy induced by the Coriolis force is visible at all scales. Finally, we identify two different wavenumber ranges in which anisotropy behaves differently, and show that if the Rossby number is not too low the characteristic lenghscale separating them is the one at which rotation and dissipation effects balance.