Parametric instability in warped astrophysical discs: growth, saturation, and feedback
Parametric instability in warped astrophysical discs: growth, saturation, and feedback
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扭曲天体物理盘中的参数不稳定性：生长、饱和和反馈
DOI：
10.1093/mnras/stad211
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发表时间：
2023
影响因子：
4.8
通讯作者：
Fairbairn C
中科院分区：
文献类型：
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作者：
Fairbairn C
了解扭曲天体物理盘动力学的尝试引起了人们的广泛关注，这主要是由于观测到的扭曲系统目录不断增加。先前的研究表明，扭曲的演变受到起伏几何结构建立的内部流场的关键调节。这些通常被建模为层流水平剪切流，其以大约轨道频率来回振荡。然而，众所周知，这种剪切运动容易受到惯性波的流体动力学、参数不稳定性的影响，这可能会改变扭曲的动力学。虽然线性生长阶段已被很好地理解，但随后的非线性饱和与扭曲上的自洽反馈相结合尚未被研究。在这项工作中，我们使用 Fairbairn 和 Ogilvie 最近的环模型框架在拉格朗日代码 gizmo 中实现了一种新颖的数值设置。正如对不稳定性的三模式耦合分析所预测的那样，我们在模拟中正式识别了几种局部增长模式，并发现与理论增长率相当一致。我们将饱和机制理解为一种破波过程，它首先抑制较短波长参量耦合的增长，同时允许最长模式主导最终的准稳态、波状湍流。将能量从扭曲传输到小尺度的雷诺应力可以使用依赖于时间的各向异性粘性 α 模型进行有效建模，该模型密切捕捉扭曲的幅度和相位演化。因此，该模型可能有助于为未来的全球研究提供信息，这些研究很常见，但通常不能解决参数不稳定性问题。
Attempts to understand the dynamics of warped astrophysical discs have garnered significant attention, largely motivated by the growing catalogue of observed distorted systems. Previous studies have shown that the evolution of the warp is crucially regulated by the internal flow fields established by the undulating geometry. These are typically modelled as laminar horizontal, shearing flows which oscillate back and forth at approximately the orbital frequency. However this shearing motion is known to be susceptible to a hydrodynamic, parametric instability of inertial waves which might modify the warped dynamics. Whilst the linear growth phase is well understood, the subsequent non-linear saturation combined with the self-consistent feedback onto the warp has not been studied. In this work, we implement a novel numerical setup using the recent ring model framework of Fairbairn and Ogilvie, within the Lagrangian codegizmo. We formally identify several locally growing modes in the simulation, as predicted by a three-mode coupling analysis of the instability, and find decent agreement with the theoretical growth rates. We understand the saturation mechanism as a wave breaking process which suppresses the growth of shorter wavelength parametric couplings first, whilst allowing the longest mode to dominate the final quasi-steady, wave-like turbulence. The Reynolds stresses, transporting energy from the warp to the small scales, can be effectively modelled using a time-dependent, anisotropic viscous alpha model which closely captures the amplitude and phase evolution of the warp. Consequently, this model might help inform future global studies which are commonplace but typically do not resolve the parametric instability.