Supersonic turbulence in shock-bound interaction zones - I. Symmetric settings
Supersonic turbulence in shock-bound interaction zones - I. Symmetric settings
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激波相互作用区中的超音速湍流 - I. 对称设置
DOI：
10.1051/0004-6361:20053898
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发表时间：
2006
影响因子：
6.5
通讯作者：
R. Walder
中科院分区：
文献类型：
--
作者：
D. Folini;R. Walder
碰撞高超声速流在许多天体物理物体中起着决定性的作用。例如，它们有助于分子云结构、o型星的x射线发射、星系片的分化、风驱动结构的出现，或者可能是γ射线暴的迅速发射。我们的目的是深入研究这种流动的湍流相互作用区，冷致密层（CDL）。在本文中，我们关注二维平面平行等温板的理想模型和对称设置，其中两种流动具有相同的参数。我们用迎风马赫数（$5 < M_{{\rm u}} < 90$）进行了一组高分辨率模拟。
我们发现CDL形状不规则，内部呈片状和丝状。这些结构的大小随着$\ell_{{\rm cdl}}$， CDL的扩展而增加。平均而言，但不是每个时刻，解决方案几乎是自相似的，只依赖于$M_{{\rm u}}$。给出了相应的解析表达式，并根据仿真结果导出了数值常数。特别是，我们发现均方根马赫数的比例为$M_{{\rm rms}} \approx 0.2~M_{{\rm u}}$。平均密度$\rho_{{\rm m}} \approx 30~\rho_{{\rm u}}$与$M_{{\rm u}}$无关。在激波通道中幸存下来的逆风动能的比例$f_{{\rm eff}}$为$f_{{\rm eff}}= 1 - M_{{\rm rms}}^{-0.6}$。如果逆风流动参数从CDL的一侧到另一侧不同，则这种依赖性仍然存在，这表明CDL内部的湍流及其驱动是相互耦合的。另一个发现指向相同的方向，即围震的自相关长度与CDL内湍流的特征长度尺度成正比。上游马赫数越大，CDL扩展速度越快，限制界面相对于上游流动方向的倾斜度越小，驱动效率越高，相对于CDL的扩展，内部结构越精细。
Colliding hypersonic flows play a decisive role in many astrophysical objects. They contribute, for example, to the molecular cloud structure, the X-ray emission of O-stars, differentiation of galactic sheets, appearance of wind-driven structures, or, possibly, to the prompt emission of γ -ray bursts. Our intention is thorough investigation of the turbulent interaction zone of such flows, the cold dense layer (CDL). In this paper, we focus on the idealized model of a 2D plane parallel isothermal slab and on symmetric settings, where both flows have equal parameters. We performed a set of high-resolution simulations with upwind Mach-numbers, $5 < M_{{\rm u}} < 90$.
We find that the CDL is irregularly shaped and has a patchy and filamentary interior. The size of these structures increases with $\ell_{{\rm cdl}}$, the extension of the CDL. On average, but not at each moment, the solution is nearly self-similar and only depends on $M_{{\rm u}}$. We give the corresponding analytical expressions, with numerical constants derived from the simulation results. In particular, we find the root-mean-square Mach-number to scale as $M_{{\rm rms}} \approx 0.2~M_{{\rm u}}$. The mean density, $\rho_{{\rm m}} \approx 30~\rho_{{\rm u}}$ is independent of $M_{{\rm u}}$. The fraction $f_{{\rm eff}}$ of the upwind kinetic energy that survives shock passage scales as $f_{{\rm eff}}= 1 - M_{{\rm rms}}^{-0.6}$. This dependence persists if the upwind flow parameters differ from one side to the other of the CDL, indicating that the turbulence within the CDL and its driving are mutually coupled. Another finding points in the same direction, namely that the auto-correlation length of the confining shocks and the characteristic length scale of the turbulence within the CDL are proportional. Larger upstream Mach-numbers lead to a faster expanding CDL, confining interfaces that are less inclined with respect to the upstream flow direction, more efficient driving, and finer interior structure with respect to the extension of the CDL.