Self-organization of local streamline structures and energy transfer rate in compressible plasma turbulence

TL;DR

This paper investigates how local streamline topology influences energy transfer in plasma turbulence, revealing different behaviors in compressible and incompressible regimes through simulations.

Contribution

It introduces a detailed analysis of the relationship between streamline topology and energy cascade rates in compressible plasma turbulence using advanced simulation techniques.

Findings

Incompressible fluctuations transfer energy mainly through strain and stable vortical structures.

Compressible fluctuations show no clear topological pattern in energy transfer.

The sign of volumetric compression or expansion influences the energy cascade direction.

Abstract

We examine how local streamline topology and energy cascade rate self-organize in plasma turbulence for both compressible and incompressible regimes. Using a fully-compressible Hall-magnetohydrodynamic simulation, we quantify the subgrid-scale energy transfer and analyze its relationship to streamline structures by means of grandient tensor geometric invariants of the velocity field. Our results highlight how streamline topology is crucial for diagnosing turbulence: for nearly-incompressible fluctuations the energy is primarily transferred to smaller scales through strain-dominated and stable-vortical structures, while is back-transferred towards larger scales through unstable-vortical structures. Compressible fluctuations, on the contrary, do not show a clear topological selection of the energy transfer since the overall direction of the local cascade rate is found to be determined by the sign of $-\nabla\cdot u$ (plasma volumetric compression or expansion).