Effects of Numerical Resolution on Simulated Cloud-Wind Interactions

TL;DR

This study examines how numerical resolution affects the simulation of cloud-wind interactions, revealing that resolution impacts cloud survival and acceleration differently depending on the physical regime, with no universal resolution threshold.

Contribution

The paper provides a systematic analysis of resolution effects on cloud evolution in hydrodynamical simulations, highlighting the need for scenario-specific resolution considerations.

Findings

Cloud survival depends on resolution, with convergence at 4 cells per cloud radius in radiative subsonic cases.

Cloud destruction and velocity are resolution-dependent in supersonic regimes, not converged even at 48 cells per radius.

A simple model shows ram pressure accelerates clouds before mixing dominates as the main acceleration mechanism.

Abstract

Mixing by hydrodynamical instabilities plays a key role in cloud-wind interactions, causing cloud destruction in the adiabatic limit and facilitating cloud survival with efficient radiative cooling. However, the rate of mixing in numerical simulations is sensitive to the smallest resolved scale, and the relationship between resolution and cloud evolution is under-explored. Using a set of cloud-crushing simulations, we investigate the effects of numerical resolution on cloud survival and acceleration. Modeling both adiabatic and radiative cases, in a subsonic and supersonic wind, we find that cloud survival and velocity does depend on the numerical resolution, however, no single resolution requirement can be applied to all scenarios. In the radiative subsonic case, we find that mass growth and acceleration appear converged at only 4 cells per cloud radius. Conversely, in the supersonic regime, we see a clear dependence of cloud destruction and velocity on resolution that is not converged even at 48 cells per cloud radius, implying that accurately capturing cloud destruction may require higher resolution than capturing growth. We also present a simple model illustrating how ram pressure accelerates cool clouds at early times before mixing kicks in as an acceleration mechanism.