arXiv 2209.040642022-09-09physics.plasm-ph

湍流模型降阶中的边际性问题

The Problem of Marginality in Model Reductions of Turbulence

C. Gillot, G. Dif-Pradalier, Y. Sarazin, C. Bourdelle, Y. Camenen, J. Citrin, X. Garbet, Ph. Ghendrih, V. Grandgirard, P. Manas, F. Widmer

DOI：: 10.1088/1361-6587/acc276

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AI总结：

本文通过对比有/无尺度分离的湍流模型，发现简化模型在远高于阈值时表现良好，但在近边际稳定区会显著低估通量，并提出改进方案。

摘要：

具有尺度分离的简化准线性（QL）和非线性（梯度驱动）模型通常用于解释实验并预测磁化等离子体中的湍流输运水平，本文将其与无尺度分离的非线性模型（通量驱动）进行对比检验。在采用玻尔兹曼电子的条件下，研究了两种不同的湍流状态——远高于阈值或接近边际稳定性。简化模型的成功尤其取决于对非线性通量的再现。在高于阈值时，模型之间表现出良好的一致性，而简化模型在接近边际性时会显著低估通量，忽略了中尺度流组织和湍流自对流。本文讨论了改进简化模型的建设性方案。

英文摘要：

Reduced quasilinear (QL) and nonlinear (gradient-driven) models with scale separations, commonly used to interpret experiments and to forecast turbulent transport levels in magnetised plasmas are tested against nonlinear models without scale separations (flux-driven). Two distinct regimes of turbulence -- either far above threshold or near marginal stability -- are investigated with Boltzmann electrons. The success of reduced models especially hinges on the reproduction of nonlinear fluxes. Good agreement between models is found above threshold whilst reduced models would significantly underpredict fluxes near marginality, overlooking mesoscale flow organisation and turbulence self-advection. Constructive prescriptions whereby to improve reduced models is discussed.

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