Turbulence is a key ingredient for the evolution of the intracluster medium, whose properties can be predicted with high-resolution numerical simulations. We present initial results on the generation of solenoidal and compressive turbulence in the intracluster medium during the formation of a small-size cluster using highly resolved, non-radiative cosmological simulations, with a refined monitoring in time. In this first of a series of papers, we closely look at one simulated cluster whose formation was distinguished by a merger around z ~ 0.3.We separate laminar gas motions, turbulence and shocks with dedicated filtering strategies and distinguish the solenoidal and compressive components of the gas flows using Hodge-Helmholtz decomposition. Solenoidal turbulence dominates the dissipation of turbulent motions (~95 per cent) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important (~30 per cent of the total) only at large radii (≥0.5rvir) and close to merger events.We show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence. All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive, stretching and advective terms) are found to be significant, but in amounts that vary with time and location. Two important trends for the growth of enstrophy in our simulation are identified: first, enstrophy is continuously accreted into the cluster from the outside, and most of that accreted enstrophy is generated near the outer accretion shocks by baroclinic and compressive processes. Secondly, in the cluster interior vortex, stretching is dominant, although the other terms also contribute substantially.
Bibliographical noteFunding Information:
Computations described in thiswork were performed using the ENZO code (http://enzo-project.org), which is the product of a collaborative effort of scientists at many universities and national laboratories. We gratefully acknowledge the ENZO development group for providing extremely helpful and well-maintained online documentation and tutorials. The reported simulations and most of the analysis were carried out using resources at the University of Minnesota Supercomputing Institute (MSI). FV acknowledges financial support from the grant VA 876-3/1 and partial financial support from the FOR1254 Research Unit of the German Science Foundation (DFG). TWJ acknowledges NSF support through grant AST121159. GB acknowledges partial support from PRIN-INAF 2014. DR was supported by the National Research Foundation of Korea through grants 2016R1A5A1013277 and 2014M1A7A1A03029872.
© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
- Galaxies: clusters: general
- Intergalactic medium
- Large-scale structure of Universe
- Methods: numerical