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We compare two different codes for simulations of cosmological structureformation to investigate the sensitivity of hydrodynamical instabilities tonumerics, in particular, the hydro solver and the application of adaptive meshrefinement (AMR). As a simple test problem, we consider an initially sphericalgas cloud in a wind, which is an idealized model for the merger of a subclusteror galaxy with a big cluster. Based on an entropy criterion, we calculate themass stripping from the subcluster as a function of time. Moreover, theturbulent velocity field is analyzed with a multi-scale filtering technique. Wefind remarkable differences between the commonly used PPM solver withdirectional splitting in the Enzo code and an unsplit variant of PPM in the Nyxcode, which demonstrates that different codes can converge to systematicallydifferent solutions even when using uniform grids. For the test case of anunbound cloud, AMR simulations reproduce uniform-grid results for the massstripping quite well, although the flow realizations can differ substantially.If the cloud is bound by a static gravitational potential, however, we findstrong sensitivity to spurious fluctuations which are induced at the cutoffradius of the potential and amplified by the bow shock. This gives rise tosubstantial deviations between uniform-grid and AMR runs performed with Enzo,while the mass stripping in Nyx simulations of the subcluster is nearlyindependent of numerical resolution and AMR. Although many factors related tonumerics are involved, our study indicates that unsplit solvers with advancedflux limiters help to reduce grid effects and to keep numerical noise undercontrol, which is important for hydrodynamical instabilities and turbulentflows.

Influence of adaptive mesh refinement and the hydro solver on shear-induced mass stripping in a minor-merger scenario