TURBULENT TRANSPORT IN A STRONGLY STRATIFIED FORCED SHEAR LAYER WITH THERMAL DIFFUSION
TURBULENT TRANSPORT IN A STRONGLY STRATIFIED FORCED SHEAR LAYER WITH THERMAL DIFFUSION
复制标题
具有热扩散的强分层受迫剪切层中的湍流输运
DOI：
10.3847/0004-637x/821/1/49
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
L. Kulenthirarajah
中科院分区：
文献类型：
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作者：
P. Garaud;L. Kulenthirarajah
这项工作提出了在强分层、热扩散环境中剪切引起的湍流引起的热量和化学物质传输的数值结果。在这种情况下驱动的剪切不稳定性有时被称为“长期”剪切不稳定性，并且当流动的理查森数很大时（只要佩克莱数很小）就会发生。我们已经确定了一组简单的标准来确定这些不稳定性是否会发生。一般来说，我们发现当流体的热扩散率非常大（通常大于 1014 cm2 s−1）时，它们可能是相关的，例如在大质量恒星的外层（M ≥ 10 M⊙）就是这种情况。使用一个简单的模型设置，其中剪切力由空间正弦、恒定幅度的体积力驱动，我们已经确定了从有效非分层到非常强烈分层的几种状态，每种状态都有自己的一组动力学特性。然而，除非系统处于两个极端状态之一（有效非分层或完全稳定），否则我们发现 (1) 只有约 10% 的输入功率用于热传输，而其余 90% 被粘性耗散； (2) 有效成分混合系数可以通过 Zahn 模型很好地近似，其中 D ≃ 0.02κT/J，其中 κT 是热扩散率，J 是理查森数。然而，这些结果需要通过不同模型设置和更高有效雷诺数的模拟来证实。
This work presents numerical results on the transport of heat and chemical species by shear-induced turbulence in strongly stratified, thermally diffusive environments. The shear instabilities driven in this regime are sometimes called “secular” shear instabilities, and can take place when the Richardson number of the flow is large, provided the Péclet number is small. We have identified a set of simple criteria to determine whether these instabilities can take place or not. Generally speaking, we find that they may be relevant whenever the thermal diffusivity of the fluid is very large (typically larger than 1014 cm2 s−1), which is the case in the outer layers of high-mass stars (M ≥ 10 M⊙), for instance. Using a simple model setup in which the shear is forced by a spatially sinusoidal, constant-amplitude body-force, we have identified several regimes ranging from effectively unstratified to very strongly stratified, each with its own set of dynamical properties. Unless the system is in one of the two extreme regimes (effectively unstratified or completely stable), however, we find that (1) only about 10% of the input power is used toward heat transport, while the remaining 90% is viscously dissipated; (2) that the effective compositional mixing coefficient is well-approximated by the model of Zahn, with D ≃ 0.02κT/J where κT is the thermal diffusivity and J is the Richardson number. These results need to be confirmed, however, with simulations in different model setups and at higher effective Reynolds number.