Role of helicity for large- and small-scale turbulent fluctuations.
Role of helicity for large- and small-scale turbulent fluctuations.
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DOI：
10.1103/physreve.92.051002
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发表时间：
2015-06
期刊：
影响因子：
--
通讯作者：
G. Sahoo;F. Bonaccorso;Luca Biferale
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文献类型：
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作者：
G. Sahoo;F. Bonaccorso;Luca Biferale
研究了螺旋度对湍流动力学的影响。目的是解开螺旋度在确定惯性范围内能量传递的方向、强度和波动中的作用。我们引入了一个外部参数α来控制正负螺旋极化傅里叶模式数量的不匹配。我们给出了Navier-Stokes方程的直接数值模拟，从完全对称情况（α=0）到完全不对称情况（α=1），当只有一个符号的螺旋模态存在。我们发现能量级联的方向与α有一个奇异的依赖关系，只要存在几个具有不同螺旋极性的模态，就会测量到正的正向通量。小尺度波动对模态降低的程度也非常敏感，导致在α ~ 0.1值时间歇性消失。如果分析仅限于具有相同螺旋符号的模态集，则属于少数模态集的间歇性消失，并且与原始Navier-Stokes方程的间歇性接近。
The effects of the helicity on the dynamics of turbulent flows are investigated. The aim is to disentangle the role of helicity in fixing the direction, the intensity, and the fluctuations of the energy transfer across the inertial range of scales. We introduce an external parameter α that controls the mismatch between the number of positive and negative helically polarized Fourier modes. We present direct numerical simulations of Navier-Stokes equations from the fully symmetrical case, α=0, to the fully asymmetrical case, α=1, when only helical modes of one sign survive. We found a singular dependency of the direction of the energy cascade on α, measuring a positive forward flux as soon as only a few modes with different helical polarities are present. Small-scale fluctuations are also strongly sensitive to the degree of mode reduction, leading to a vanishing intermittency already for values of α∼0.1. If the analysis is restricted to sets of modes with the same helicity sign, intermittency is vanishing for the modes belonging to the minority set, and it is close to that measured on the original Navier-Stokes equations for the other set.