不可压缩导电流体逐点零螺旋度三维steady flow产生磁场
Magnetic field generation by pointwise zero-helicity three-dimensional steady flow of incompressible electrically conducting fluid
摘要：
本文介绍了六类三维空间周期定常螺线管流，它们的动力学螺旋度密度在任意点都为零。四个家庭是分析定义。四个族中的流动具有零螺旋度谱。从五个家庭的样本流被用来证明数字，无论是零动力学螺旋密度，也不是零螺旋谱禁止产生大规模的磁场由两个最突出的发电机机制：磁$α$效应和负涡扩散。我们的计算还证明，这种流动往往产生足够小的磁分子扩散率的小尺度场。这些发现表明，动力学螺旋度和螺旋度谱不是控制流的发电机特性的量，无论尺度分离是否存在。
英文摘要：
We introduce six families of three-dimensional space-periodic steady solenoidal flows, whose kinetic helicity density is zero at any point. Four families are analytically defined. Flows in four families have zero helicity spectrum. Sample flows from five families are used to demonstrate numerically that neither zero kinetic helicity density, nor zero helicity spectrum prohibit generation of large-scale magnetic field by the two most prominent dynamo mechanisms: the magnetic $α$-effect and negative eddy diffusivity. Our computations also attest that such flows often generate small-scale field for sufficiently small magnetic molecular diffusivity. These findings indicate that kinetic helicity and helicity spectrum are not the quantities controlling the dynamo properties of a flow regardless of whether scale separation is present or not.
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