TURBULENCE IN THE INTERGALACTIC MEDIUM: SOLENOIDAL AND DILATATIONAL MOTIONS AND THE IMPACT OF NUMERICAL VISCOSITY
TURBULENCE IN THE INTERGALACTIC MEDIUM: SOLENOIDAL AND DILATATIONAL MOTIONS AND THE IMPACT OF NUMERICAL VISCOSITY
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DOI：
10.1088/0004-637x/777/1/48
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发表时间：
2013-08
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影响因子：
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通讯作者：
Weishan Zhu;Longlong Feng;Yinhua Xia;Chi-Wang Shu;Q. Gu;L. Fang
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作者：
Weishan Zhu;Longlong Feng;Yinhua Xia;Chi-Wang Shu;Q. Gu;L. Fang
我们使用一套宇宙学流体动力学模拟，运行两个固定的网格代码，研究星系际介质（IGM）的螺线管和湍流运动的性质和数值粘性对ΛCDM宇宙中湍流的影响。这两种编码的区别仅在于空间差分离散化。我们发现：（1）涡旋运动从z = 2开始迅速增长，在z = 0时达到100 km s-1-90 km s-1。同时，小尺度压缩比rCS从0.84下降到0.47，表明在z = 0时具有可比的涡旋和压缩运动。(2)螺线管速度的功率谱有两个区域，分别为k-0.89和k-2.02，而总速度和湍流速度分别遵循k-1.88和k-2.20的标度。IGM湍流可以包含两个不同的阶段，超声速和后超声速阶段。(3)当ρB = 10-100或T < 105.5 K（z = 0.0）时，用涡动能测量的非热压力支持与热压力相当。重子分数与宇宙平均值的偏差与湍流压力的支持有初步的正相关。(4)相对较高的数值粘性会更有效地将IGM的压缩运动和涡旋运动耗散为热能，导致较不发达的涡度，显著缩短的惯性范围，并导致气体吸积热历史中不可忽略的不确定性。由于z = 2，数值粘性显著地抑制了群外区域的激波，这可能直接导致了两个代码之间的不同湍流水平。
We use a suite of cosmological hydrodynamical simulations, run by two fixed grid codes, to investigate the properties of solenoidal and dilatational motions of the intergalactic medium (IGM) and the impact of numerical viscosity on turbulence in an ΛCDM universe. The codes differ only in the spatial difference discretization. We find that (1) The vortical motion grows rapidly since z = 2 and reaches ∼10 km s−1–90 km s−1 at z = 0. Meanwhile, the small-scale compressive ratio rCS drops from 0.84 to 0.47, indicating comparable vortical and compressive motions at z = 0. (2) Power spectra of the solenoidal velocity possess two regimes, ∝k−0.89 and ∝k−2.02, while the total and dilatational velocity follow the scaling k−1.88 and k−2.20, respectively, in the turbulent range. The IGM turbulence may contain two distinct phases, the supersonic and post-supersonic phases. (3) The non-thermal pressure support, measured by the vortical kinetic energy, is comparable with the thermal pressure for ρb ≃ 10–100, or T < 105.5 K at z = 0.0. The deviation of the baryon fraction from the cosmic mean shows a preliminary positive correlation with the turbulence pressure support. (4) A relatively higher numerical viscosity would dissipate both the compressive and vortical motions of the IGM into thermal energy more effectively, resulting in less developed vorticity, remarkably shortened inertial range, and leading to a non-negligible uncertainty in the thermal history of gas accretion. Shocks in regions outside of clusters are significantly suppressed by numerical viscosity since z = 2, which may directly cause the different levels of turbulence between the two codes.