The Cosmological Simulation Code OpenGadget3 -- Implementation of Meshless Finite Mass

TL;DR

This paper introduces a Meshless Finite Mass implementation in OpenGadget3, demonstrating improved mixing, stability, and convergence in simulations of turbulence and cosmological structures, with robust performance in complex astrophysical tests.

Contribution

The paper presents a novel MFM implementation in OpenGadget3, enhancing simulation accuracy and stability for astrophysical fluid dynamics, especially in subsonic turbulence.

Findings

MFM outperforms SPH in mixing and convergence.

MFM accurately captures velocity power spectra in turbulence.

The solver remains robust in cosmological simulations.

Abstract

Subsonic turbulence plays a major role in determining properties of the intra cluster medium (ICM). We introduce a new Meshless Finite Mass (MFM) implementation in OpenGadget3 and apply it to this specific problem. To this end, we present a set of test cases to validate our implementation of the MFM framework in our code. These include but are not limited to: the soundwave and Kepler disk as smooth situations to probe the stability, a Rayleigh-Taylor and Kelvin-Helmholtz instability as popular mixing instabilities, a blob test as more complex example including both mixing and shocks, shock tubes with various Mach numbers, a Sedov blast wave, different tests including self-gravity such as gravitational freefall, a hydrostatic sphere, the Zeldovich-pancake, and a $10^{15}M_{\odot}$ galaxy cluster as cosmological application. Advantages over SPH include increased mixing and a better convergence behavior. We demonstrate that the MFM-solver is robust, also in a cosmological context. We show evidence that the solver performs extraordinarily well when applied to decaying subsonic turbulence, a problem very difficult to handle for many methods. MFM captures the expected velocity power spectrum with high accuracy and shows a good convergence behavior. Using MFM or SPH within OpenGadget3 leads to a comparable decay in turbulent energy due to numerical dissipation. When studying the energy decay for different initial turbulent energy fractions, we find that MFM performs well down to Mach numbers $\mathcal{M}\approx 0.01$. Finally, we show how important the slope limiter and the energy-entropy switch are to control the behavior and the evolution of the fluids.