Sensitivity of non-radiative cloud-wind interactions to the hydrodynamics solver

TL;DR

This study compares seven hydrodynamics solvers in simulating cloud-wind interactions, revealing significant differences in results and emphasizing the importance of solver choice in astrophysical simulations.

Contribution

It systematically evaluates the impact of various hydrodynamics solvers on cloud-wind interaction simulations, highlighting discrepancies and the need for solver robustness checks.

Findings

SPH methods show slower cloud dispersal at higher density contrasts.

Predictions for intermediate-temperature gas vary significantly between solvers.

Convergence rates differ notably among the hydrodynamics methods.

Abstract

Cloud-wind interactions are common in the interstellar and circumgalactic media. Many studies have used simulations of such interactions to investigate the effect of particular physical processes, but the impact of the choice of hydrodynamics solver has largely been overlooked. Here we study the cloud-wind interaction, also known as the "blob test", using seven different hydrodynamics solvers: Three flavours of SPH, a moving mesh, adaptive mesh refinement and two meshless schemes. The evolution of masses in dense gas and intermediate-temperature gas, as well as the covering fraction of intermediate-temperature gas, are systematically compared for initial density contrasts of 10 and 100, and five numerical resolutions. To isolate the differences due to the hydrodynamics solvers, we use idealised non-radiative simulations without physical conduction. We find large differences between these methods. SPH methods show slower dispersal of the cloud, particularly for the higher density contrast, but faster convergence, especially for the lower density contrast. Predictions for the intermediate-temperature gas differ particularly strongly, also between non-SPH codes, and converge most slowly. We conclude that the hydrodynamical interaction between a dense cloud and a supersonic wind remains an unsolved problem. Studies aiming to understand the physics or observational signatures of cloud-wind interactions should test the robustness of their results by comparing different hydrodynamics solvers.