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首页> 外文期刊>Physics of fluids >Evidence for Bolgiano-Obukhov scaling in rotating stratified turbulence using high-resolution direct numerical simulations
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Evidence for Bolgiano-Obukhov scaling in rotating stratified turbulence using high-resolution direct numerical simulations

机译：使用高分辨率直接数值模拟的旋转分层湍流中Bolgiano-Obukhov缩放的证据

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We report results on rotating stratified turbulence in the absence of forcing and with large-scale isotropic initial conditions using direct numerical simulations computed on grids of up to 4096 (3) points. The Reynolds and Froude numbers are, respectively, equal to Re = 5.4 x 10 (4) and Fr = 0.0242. The ratio of the Brunt-Vaisala to the inertial wave frequency, N/f, is taken to be equal to 4.95, a choice appropriate to model the dynamics of the southern abyssal ocean at mid latitudes. This gives a global buoyancy Reynolds number R-B = ReFr2 approximate to 32, a value sufficient for some isotropy to be recovered in the small scales beyond the Ozmidov scale, but still moderate enough that the intermediate scales where waves are prevalent are well resolved. We concentrate on the large-scale dynamics, for which we find a spectrum compatible with the Bolgiano-Obukhov scaling. This scaling is also found for geostrophically balanced initial conditions on a run at a lower resolution and hence lower R-B approximate to 4. Furthermore, we confirm that the Froude number based on a typical vertical length scale is of order unity, with strong gradients in the vertical. Two characteristic scales emerge from this computation and are identified from sharp variations in the spectral distribution of either total energy or helicity. A spectral break is also observed at a scale at which the partition of energy between the kinetic and potential modes changes abruptly, and beyond which a Kolmogorov-like spectrum recovers. Large slanted layers are ubiquitous in the flow, in the velocity and temperature fields, with local overturning events indicated by small local Richardson numbers and strong localized vortex tangles. Finally, a small large-scale enhancement of energy directly attributable to the effect of rotation is also observed. (C) 2015 AIP Publishing LLC.
机译：我们使用在多达4096（3）个点的网格上计算的直接数值模拟，报告了在没有强迫和大尺度各向同性初始条件下旋转分层湍流的结果。雷诺数和弗洛德数分别等于Re = 5.4 x 10（4）和Fr = 0.0242。 Brunt-Vaisala与惯性波频率的比率N / f被认为等于4.95，该选择适合于模拟中纬度南部深渊海洋的动力学。这使总的浮力雷诺数R-B = ReFr2大约为32，该值足以在Ozmidov刻度以外的小刻度上恢复一些各向同性，但仍足够适中，从而可以很好地解决波浪普遍存在的中间刻度。我们专注于大规模动力学，为此我们发现了与Bolgiano-Obukhov缩放比例兼容的频谱。在较低分辨率下运行时，在地转平衡的初始条件下也发现了这种标度，因此，RB较低，近似为4。此外，我们确认基于典型垂直长度标度的Froude数为1阶，并且在垂直。从该计算中得出两个特征标度，并从总能量或螺旋度的光谱分布的急剧变化中识别出来。还观察到一个光谱断裂，该断裂的尺度是动力学模式和势能模式之间的能量分配突然变化，并且超过此范围，类似科尔莫哥罗夫的光谱得以恢复。流动，速度和温度场中普遍存在大的倾斜层，局部的翻转事件由小的局部理查森数和强的局部涡缠结表示。最后，还观察到直接归因于旋转作用的能量的小范围大规模增强。 （C）2015 AIP Publishing LLC。

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