Modelling coexisting GSF and shear instabilities in rotating stars
Modelling coexisting GSF and shear instabilities in rotating stars
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模拟旋转恒星中共存的 GSF 和剪切不稳定性
DOI：
10.1093/mnras/stab1927
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发表时间：
2021
影响因子：
4.8
通讯作者：
Garaud, Pascale
中科院分区：
文献类型：
--
作者：
Chang, Eonho;Garaud, Pascale
Zahn广泛使用的旋转剪切引起的湍流混合模型最近在非旋转剪切流中得到了验证（有一些警告）。然而，目前尚不清楚他的模型在旋转存在的情况下是否仍然有效，即使这是其最初的目的。此外，在旋转流体中会出现新的不稳定性，例如Goldreich-Schubert-Schuberke（GSF）不稳定性。当一个以上的不稳定性可以被激发时，哪种不稳定性占主导地位，以及它们如何相互影响，是本文回答的开放性问题。要做到这一点，我们使用直接的数值模拟扩散分层剪切流在旋转的三重周期笛卡尔域位于赤道的星星。我们发现，无论是GSF不稳定性或剪切不稳定性往往接管其他控制系统，这表明恒星演化模型只需要有一个混合处方为每个人的不稳定性，连同一个标准，以确定哪一个占主导地位。然而，我们也发现，它并不总是容易预测的不稳定'赢'给定的输入参数，因为扩散剪切不稳定是亚临界的，只有发生，如果有一个有限振幅的湍流'引物'播种it. Interesting，我们发现，GSF不稳定在某些情况下可以发挥这个引物的作用，从而提供了一条途径，激发亚临界剪切不稳定。这也可以驱动可以观察到的弛豫振荡。最后，我们提出了一个新的模型混合在赤道地区的恒星辐射区由于差分旋转。
Zahn’s widely used model for turbulent mixing induced by rotational shear has recently been validated (with some caveats) in non-rotating shear flows. It is not clear, however, whether his model remains valid in the presence of rotation, even though this was its original purpose. Furthermore, new instabilities arise in rotating fluids, such as the Goldreich–Schubert–Fricke (GSF) instability. Which instability dominates when more than one can be excited, and how they influence each other, were open questions that this paper answers. To do so, we use direct numerical simulations of diffusive stratified shear flows in a rotating triply periodic Cartesian domain located at the equator of a star. We find that either the GSF instability or the shear instability tends to take over the other in controlling the system, suggesting that stellar evolution models only need to have a mixing prescription for each individual instability, together with a criterion to determine which one dominates. However, we also find that it is not always easy to predict which instability ‘wins’ for given input parameters, because the diffusive shear instability is subcritical, and only takes place if there is a finite-amplitude turbulence ‘primer’ to seed it. Interestingly, we find that the GSF instability can in some cases play the role of this primer, thereby providing a pathway to excite the subcritical shear instability. This can also drive relaxation oscillations, which may be observable. We conclude by proposing a new model for mixing in the equatorial regions of stellar radiative zones due to differential rotation.
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