Vorticity of Intergalactic Medium Velocity Field on Large Scales

Zhu, Weishan; Feng, Long-Long; Fang, Li‐Zhi

doi:10.1088/0004-637x/712/1/1

Cited by 45 publications

(101 citation statements)

References 47 publications

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“…This can be understood as a consequence of the nonlinear term in the closure for the turbulence energy flux. Also the estimate of turbulent pressure effects using the rate of strain and the vorticity of the resolved flow that is put forward by Zhu et al (2010) is incomplete because they do not distinguish between the contributions from the resolved flow and from the subgrid scales. The predictions from both approaches with regard to turbulence in the intergalactic medium are compared in ongoing work (Iapichino et al 2011).…”

Section: Resultsmentioning

confidence: 99%

A fluid-dynamical subgrid scale model for highly compressible astrophysical turbulence

Schmidt

Federrath

2011

A&A

110

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Context. Compressible turbulence influences the dynamics of the interstellar and the intergalactic medium over a vast range of length scales. In numerical simulations, phenomenological subgrid scale (SGS) models are used to describe particular physical processes below the grid scale. In most cases, these models do not cover fluid-dynamical interactions between resolved and unresolved scales, or the employed SGS model is not applicable to turbulence in the highly compressible regime. Aims. We formulate and implement the Euler equations with SGS dynamics and provide numerical tests of an SGS turbulence energy model that predicts the turbulent pressure of unresolved velocity fluctuations and the rate of dissipation for highly compressible turbulence. Methods. We tested closures for the turbulence energy cascade by filtering data from high-resolution simulations of forced isothermal and adiabatic turbulence. Optimal properties and an excellent correlation are found for a linear combination of the eddy-viscosity closure that is employed in LES of weakly compressible turbulence and a term that is nonlinear in the Jacobian matrix of the velocity. Using this mixed closure, the SGS turbulence energy model is validated in LES of turbulence with stochastic forcing. Results. It is found that the SGS model satisfies several important requirements: 1. The mean SGS turbulence energy follows a power law for varying grid scale. 2. The root mean square (rms) Mach number of the unresolved velocity fluctuations is proportional to the rms Mach number of the resolved turbulence, independent of the forcing. 3. The rate of dissipation and the turbulence energy flux are constant. Moreover, we discuss difficulties with direct estimates of the turbulent pressure and the dissipation rate on the basis of resolved flow quantities that have recently been proposed. Conclusions. In combination with the energy injection by stellar feedback and other unresolved processes, the proposed SGS model is applicable to a variety of problems in computational astrophysics. By computing the SGS turbulence energy, the treatment of star formation and stellar feedback in galaxy simulations can be improved. Furthermore, we expect that the turbulent pressure on the grid scale affects the stability of gas against gravitational collapse. The influence of small-scale turbulence on emission line broadening, e.g., of O VI, in the intergalactic medium is another potential application.

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Section: Resultsmentioning

confidence: 99%

A fluid-dynamical subgrid scale model for highly compressible astrophysical turbulence

Schmidt

Federrath

2011

A&A

110

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“…Both components are used to obtain an estimate of the turbulent velocity dispersion σ turb in clusters. As opposed to previous methods for approximating the turbulent velocity and associated time scales in clusters (e. g. Norman & Bryan 1999;Dolag et al 2005;Kang et al 2007;Maier et al 2009;Zhu et al 2010), our definition of σ turb respects the three-dimensional nature of turbulence, does not depend on spherical symmetry, nor is it subject to a particular choice of a spatial smoothing length or resolution scale.…”

Section: Discussionmentioning

confidence: 99%

Hot and turbulent gas in clusters

Schmidt

Engels

Niemeyer

et al. 2016

Mon. Not. R. Astron. Soc.

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The gas in galaxy clusters is heated by shock compression through accretion (outer shocks) and mergers (inner shocks). These processes additionally produce turbulence. To analyse the relation between the thermal and turbulent energies of the gas under the influence of non-adiabatic processes, we performed numerical simulations of cosmic structure formation in a box of 152 Mpc comoving size with radiative cooling, UV background, and a subgrid scale model for numerically unresolved turbulence. By smoothing the gas velocities with an adaptive Kalman filter, we are able to estimate bulk flows toward cluster cores. This enables us to infer the velocity dispersion associated with the turbulent fluctuation relative to the bulk flow. For halos with masses above 10 13 M , we find that the turbulent velocity dispersions averaged over the warm-hot intergalactic medium (WHIM) and the intracluster medium (ICM) are approximately given by powers of the mean gas temperatures with exponents around 0.5, corresponding to a roughly linear relation between turbulent and thermal energies and transonic Mach numbers. However, turbulence is only weakly correlated with the halo mass. Since the power-law relation is stiffer for the WHIM, the turbulent Mach number tends to increase with the mean temperature of the WHIM. This can be attributed to enhanced turbulence production relative to dissipation in particularly hot and turbulent clusters.

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“…The corresponding power spectra are used to define the power spectrum decomposition, (Kitsionas et al 2009;Zhu et al 2010). In addition to the spectral properties of the velocity u(x), it is useful to investigate the scaling behavior of the velocity structure functions.…”

Section: Statistical Measuresmentioning

confidence: 99%

The impact of numerical viscosity in SPH simulations of galaxy clusters

Valdarnini

2011

A&A

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The goal of this paper is to investigate in N-body/SPH hydrodynamical cluster simulations the impact of artificial viscosity on the ICM thermal and velocity field statistical properties. To properly reduce the effects of artificial viscosity, a time-dependent artificial viscosity scheme is implemented in an SPH code in which each particle has its own viscosity parameter, whose time evolution is governed by the local shock conditions. The new SPH code is verified in a number of test problems with known analytical or numerical reference solutions and is then used to construct a large set of N-body/SPH hydrodynamical cluster simulations. These simulations are designed to study in SPH simulations the impact of artificial viscosity on the thermodynamics of the ICM and its velocity field statistical properties by comparing results extracted at the present epoch from runs with different artificial viscosity parameters, cluster dynamical states, numerical resolution, and physical modeling of the gas. Spectral properties of the gas velocity field are investigated by measuring the velocity power spectrum E(k) for the simulated clusters. Over a limited range, the longitudinal component E c (k) exhibits a Kolgomorov-like scaling ∝k −5/3 , whilst the solenoidal power spectrum component E s (k) is strongly influenced by numerical resolution effects. The dependence of the spectra E(k) on dissipative effects is found to be significant at length scales < ∼ 100−300 kpc, with viscous damping of the velocities being less pronounced in the runs with the lowest artificial viscosity. The turbulent energy density radial profile E turb (r) is strongly affected by the numerical viscosity scheme adopted in the simulations, with the turbulent-to-total energy density ratios being higher in the runs with the lowest artificial viscosity settings and lying in the range between a few percent and ∼10%. These values are in accord with the corresponding ratios extracted from previous cluster simulations based on mesh-based codes. The radial entropy profiles show a weak dependence on the artificial viscosity parameters of the simulations, with a small amount of entropy mixing being present in cluster cores. At large cluster radii, the mass correction terms to the hydrostatic equilibrium equation are affected little by the numerical viscosity of the simulations, indicating that the X-ray mass bias is already accurately estimated in standard SPH simulations. The results presented here indicate that in individual SPH cluster simulations at least N > ∼ 256 3 gas particles are necessary to provide a correct description of turbulent spectral properties over a decade in wavenumbers, whilst radial profiles of thermodynamic variables can be reliably obtained using N > ∼ 64 3 particles. Finally, simulations in which the gas can cool radiatively are characterized by the presence in the cluster inner regions of high levels of turbulence, generated by the interaction of the compact cool gas core with the ambient medium. These findings strongly support t...

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Vorticity of Intergalactic Medium Velocity Field on Large Scales

Cited by 45 publications

References 47 publications

A fluid-dynamical subgrid scale model for highly compressible astrophysical turbulence

A fluid-dynamical subgrid scale model for highly compressible astrophysical turbulence

Hot and turbulent gas in clusters

The impact of numerical viscosity in SPH simulations of galaxy clusters

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