On the relevance of subcritical hydrodynamic turbulence to accretion disk transport
On the relevance of subcritical hydrodynamic turbulence to accretion disk transport
复制标题
亚临界流体动力湍流与吸积盘输运的相关性
DOI：
10.1051/0004-6361:20053683
复制
发表时间：
2005
影响因子：
6.5
通讯作者：
P. Longaretti
中科院分区：
文献类型：
--
作者：
G. Lesur;P. Longaretti
众所周知，流体动力学非分层开普勒流在所有雷诺数下都是线性稳定的，但仍然可能通过非线性机制变得湍流。然而，近十年来，在这个问题上出现了相互矛盾的观点。我们通过剪切板极限的数值模拟重新审视了这个问题。事实证明，科里奥利力稳定流动的效果取决于流动是气旋性（剪切和旋转涡旋协同）还是反气旋（剪切和旋转涡旋竞争）；开普勒流是反气旋流。我们得到了以下结果： i/ 科里奥利力不会抑制亚临界流中的湍流；然而，与反气旋流相比，气旋流中的湍流效率更高，也更容易发现。
ii/ 雷诺数/旋转/分辨率关系已在此问题中量化。特别是，我们发现，当远离边际稳定边界时，反气旋流的分辨率要求比气旋流更严格。目前可用的计算机资源不允许数字代码到达开普勒体系。
iii/ 湍流传输效率与过渡到湍流 Rg 的雷诺数直接相关，因此 Shakura-Sunyaev 参数 $\alpha\sim 1/Rg$。这种相关性几乎与流动旋风无关。这种相关性是基于通用物理参数预期的。
iv/即使是对我们的数值数据最乐观的推断也表明，出于天体物理目的，开普勒流中的亚临界湍流传输效率太低了几个数量级。尽管在我们的初步测试中没有发现显着影响，但垂直边界条件可能在这个问题中发挥作用。
v/ 我们的结果表明，在 Taylor-Couette 设置中为类开普勒流获得的数据很大程度上受到二次流（例如埃克曼环流）的影响。
Hydrodynamic unstratified Keplerian flows are known to be linearly stable at all Reynolds numbers, but may nevertheless become turbulent through nonlinear mechanisms. However, in the last ten years, conflicting points of view have appeared on this issue. We have revisited the problem through numerical simulations in the shearing sheet limit. It turns out that the effect of the Coriolis force in stabilizing the flow depends on whether the flow is cyclonic (cooperating shear and rotation vorticities) or anticyclonic (competing shear and rotation vorticities); Keplerian flows are anticyclonic. We have obtained the following results:
i/ The Coriolis force does not quench turbulence in subcritical flows; however, turbulence is more efficient, and much more easily found, in cyclonic flows than in anticyclonic ones.
ii/ The Reynolds number/rotation/resolution relation has been quantified in this problem. In particular we find that the resolution demand, when moving away from the marginal stability boundary, is much more severe for anticyclonic flows than for cyclonic ones. Presently available computer resources do not allow numerical codes to reach the Keplerian regime.
iii/ The efficiency of turbulent transport is directly correlated to the Reynolds number of transition to turbulence Rg , in such a way that the Shakura-Sunyaev parameter $\alpha\sim 1/Rg$. This correlation is nearly independent of the flow cyclonicity. The correlation is expected on the basis of generic physical arguments.
iv/ Even the most optimistic extrapolations of our numerical data show that subcritical turbulent transport would be too inefficient in Keplerian flows by several orders of magnitude for astrophysical purposes. Vertical boundary conditions may play a role in this issue although no significant effect was found in our preliminary tests.
v/ Our results suggest that the data obtained for Keplerian-like flows in a Taylor-Couette settings are largely affected by secondary flows, such as Ekman circulation.