Two-dimensional AMR simulations of colliding flows

TL;DR

This study investigates the robustness of statistical properties in two-dimensional AMR simulations of colliding flows, focusing on how different refinement criteria affect the results and flow structures.

Contribution

It compares AMR and static-grid simulations to evaluate the impact of refinement criteria on the physical and statistical accuracy of colliding flow models.

Findings

AMR reproduces density statistics well

Refinement based on cooling time or turbulence is superior

Significant flow structure differences remain

Abstract

Colliding flows are a commonly used scenario for the formation of molecular clouds in numerical simulations. Due to the thermal instability of the warm neutral medium, turbulence is produced by cooling. We carry out a two-dimensional numerical study of such colliding flows in order to test whether statistical properties inferred from adaptive mesh refinement (AMR) simulations are robust with respect to the applied refinement criteria. We compare probability density functions of various quantities as well as the clump statistics and fractal dimension of the density fields in AMR simulations to a static-grid simulation. The static grid with 2048^2 cells matches the resolution of the most refined subgrids in the AMR simulations. The density statistics is reproduced fairly well by AMR. Refinement criteria based on the cooling time or the turbulence intensity appear to be superior to the standard technique of refinement by overdensity. Nevertheless, substantial differences in the flow structure become apparent. In general, it is difficult to separate numerical effects from genuine physical processes in AMR simulations.