Coherent structures in a turbulent environment

The role of coherent vorticity in turbulent transport in resistive drift-wave turbulence

The coherent vortex extraction method, a wavelet technique for extracting coherent vortices out of turbulent flows, is applied to simulations of resistive drift-wave turbulence in magnetized plasma (Hasegawa-Wakatani system). The aim is to retain only the essential degrees of freedom, responsible for the transport. It is shown that the radial density flux is carried by these coherent modes. In the quasi-hydrodynamic regime, coherent vortices exhibit depletion of the polarization-drift nonlinearity and vorticity strongly dominates strain, in contrast to the quasiadiabatic regime.

Magnetic Dissipation of Near-Wall Turbulent Coherent Structures in Magnetohydrodynamic Pipe Flows

Relaminarization of wall-bounded turbulent flows by means of external static magnetic fields is a long-known phenomenon in the physics of electrically conducting fluids at low magnetic Reynolds numbers. Despite the large literature on the subject, it is not yet completely clear what combination of the Hartmann ($M$) and the Reynolds number has to be used to predict the laminar-turbulent transition in channel or pipe flows fed by upstream turbulent flows free of magnetic perturbations. Relying upon standard phenomenological approaches related to mixing length and structural concepts, we put for…

三维强湍动磁化等离子体中相干结构的形成与演化

Formation and Evolution of Coherent Structures in 3D Strongly Turbulent Magnetized Plasmas

本研究综述三维强湍动磁化等离子体中相干结构的形成与演化，指出其是磁能耗散为粒子动能的关键场所，强调二维孤立研究电流片与磁重联的局限性，需结合三维真实环境建模。

Modelling stellar convective transport with plumes: I. Non-equilibrium turbulence effect in double-averaging formulation

Plumes in a convective flow are considered to be relevant to the turbulent transport in convection. The effective mass, momentum, and heat transports in the convective turbulence are investigated in the framework of time--space double averaging procedure, where a field quantity is decomposed into three parts: the spatiotemporal mean (spatial average of the time-averaged) field, the dispersion or coherent fluctuation, and the random or incoherent fluctuation. With this framework, turbulent correlations in the mean-field equations are divided into the dispersion/coherent and random/incoherent co…

Coherent structures and spectral energy transfer in turbulent plasma: a space-filter approach

Plasma turbulence at scales of the order of the ion inertial length is mediated by several mechanisms, including linear wave damping, magnetic reconnection, formation and dissipation of thin current sheets, stochastic heating. It is now understood that the presence of localized coherent structures enhances the dissipation channels and the kinetic features of the plasma. However, no formal way of quantifying the relationship between scale-to-scale energy transfer and the presence of spatial structures has so far been presented. In this letter we quantify such relationship analyzing the results …

磁绳介导的湍流磁重联

Flux-Rope Mediated Turbulent Magnetic Reconnection

提出磁绳介导的湍流磁重联新模型，强调局部相干磁结构与阿尔文视界，解释三维模拟中重联速率，适用于非零磁螺旋度情况。