Characterisation of global flow and local fluctuations in 3D SPH simulations of protoplanetary discs

TL;DR

This paper investigates whether 3D SPH simulations of protoplanetary discs can replicate observed turbulence and flow structures, revealing artificial viscosity's role in mimicking physical viscosity and turbulence.

Contribution

It demonstrates that standard artificial viscosity in SPH can act as an implicit turbulence model, reproducing key turbulent features observed in protoplanetary discs.

Findings

SPH artificial viscosity can mimic physical viscosity under specific conditions.

A threshold exists where artificial viscosity induces turbulence-like cascades.

Local turbulence coexists with global meridional circulation in the models.

Abstract

A complete and detailed knowledge of the structure of the gaseous component in protoplanetary discs is essential to the study of dust evolution during the early phases of pre-planetesimal formation. The aim of this paper is to determine if three-dimensional accretion discs simulated by the Smoothed Particle Hydrodynamics (SPH) method can reproduce the observational data now available and the expected turbulent nature of protoplanetary discs. The investigation is carried out by setting up a suite of diagnostic tools specifically designed to characterise both the global flow and the fluctuations of the gaseous disc. The main result concerns the role of the artificial viscosity implementation in the SPH method: in addition to the already known ability of SPH artificial viscosity to mimic a physical-like viscosity under specific conditions, we show how the same artificial viscosity prescription behaves like an implicit turbulence model. In fact, we identify a threshold for the parameters in the standard artificial viscosity above which SPH disc models present a cascade in the power spectrum of velocity fluctuations, turbulent diffusion and a mass accretion rate of the same order of magnitude as measured in observations. Furthermore, the turbulence properties observed locally in SPH disc models are accompanied by meridional circulation in the global flow of the gas, proving that the two mechanisms can coexist.