Turbulent heating in a stratified medium
Turbulent heating in a stratified medium
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分层介质中的湍流加热
DOI：
10.1093/mnras/stad003
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发表时间：
2023
影响因子：
4.8
通讯作者：
Ruszkowski, M.
中科院分区：
文献类型：
--
作者：
Wang, C.;Oh, S. P.;Ruszkowski, M.
有相当多的证据表明，在星系团中存在着广泛的亚音速湍流，最明显的是来自Hitomi。湍流经常被用来抵消团簇核心的辐射损失，通过直接耗散和湍流热扩散。然而，在分层介质中，浮力与径向运动相反，使湍流各向异性。这可以通过弗劳德数Fr来量化，弗劳德数Fr随着分层的增加而向内减小。我们利用与MHD湍流的类比表明，波湍流相互作用增加级联时间，降低耗散率。同样，对于给定的能量注入/耗散率，湍流速度必须高于柯尔莫哥洛夫标度。高分辨率的流体动力学模拟显示出良好的协议与的Fr的缩放，其中设置在为Fr的0.1。我们还比较了以前预测的湍流扩散系数D <$Fr 2的缩放，发现很好的协议，为Fr <$1。然而，我们发现一个不同的归一化，对应于更强的扩散抑制超过一个数量级。我们的研究结果意味着，湍流扩散更严重地抑制分层，在一个更广泛的径向范围内，比湍流耗散。因此，后者可能占主导地位。此外，这种转变意味着与以前的模型相比，抵消冷却所需的湍流速度显着更高。这些结果可能与星系群和星系团中的湍流金属扩散（同样受到抑制）以及行星大气有关。
There is considerable evidence for widespread subsonic turbulence in galaxy clusters, most notably fromHitomi. Turbulence is often invoked to offset radiative losses in cluster cores, both by direct dissipation and by enabling turbulent heat diffusion. However, in a stratified medium, buoyancy forces oppose radial motions, making turbulence anisotropic. This can be quantified via the Froude numberFr, which decreases inward in clusters as stratification increases. We exploit analogies with MHD turbulence to show that wave–turbulence interactions increase cascade times and reduce dissipation rates ϵ ∝Fr. Equivalently, for a given energy injection/dissipation rate ϵ, turbulent velocitiesumust be higher compared to Kolmogorov scalings. High-resolution hydrodynamic simulations show excellent agreement with the ϵ ∝Frscaling, which sets in forFr≲ 0.1. We also compare previously predicted scalings for the turbulent diffusion coefficientD∝ Fr2and find excellent agreement, forFr≲ 1. However, we find a different normalization, corresponding to stronger diffusive suppression by more than an order of magnitude. Our results imply that turbulent diffusion is more heavily suppressed by stratification, over a much wider radial range, than turbulent dissipation. Thus, the latter potentially dominates. Furthermore, this shift implies significantly higher turbulent velocities required to offset cooling, compared to previous models. These results are potentially relevant to turbulent metal diffusion in the galaxy groups and clusters (which is likewise suppressed), and to planetary atmospheres.