Fang Lei, Ouellette Nicholas T
Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, USA.
Phys Rev Lett. 2016 Sep 2;117(10):104501. doi: 10.1103/PhysRevLett.117.104501. Epub 2016 Aug 30.
We report measurements of the geometric alignment of the small-scale turbulent stress and the large-scale rate of strain that together lead to the net flux of energy from small scales to large scales in two-dimensional turbulence. We find that the instantaneous alignment between these two tensors is weak and, thus, that the spectral transport of energy is inefficient. We show, however, that the strain rate is much better aligned with the stress at times in the past, suggesting that the differential advection of the two is responsible for the inefficient spectral transfer. We provide evidence for this conjecture by measuring the alignment statistics conditioned on weakly changing stress history. Our results give new insight into the relationship between scale-to-scale energy transfer, geometric alignment, and advection in turbulent flows.
我们报告了对二维湍流中小尺度湍应力和大尺度应变率的几何对齐情况的测量，这两者共同导致了能量从小尺度到 大尺度的净通量。我们发现这两个张量之间的瞬时对齐较弱，因此能量的谱传输效率低下。然而，我们表明，应变率在过去的某些时刻与应力的对齐要好得多，这表明两者的差动平流是谱传输效率低下的原因。我们通过测量基于弱变化应力历史的对齐统计数据来为这一猜想提供证据。我们的结果为湍流中尺度间能量转移、几何对齐和平流之间的关系提供了新的见解。
