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Angular momentum transport in a stratified Taylor-Couette experiment with applications to accretion disks

分层泰勒-库埃特实验中的角动量传输及其在吸积盘中的应用

基本信息

批准号：
251213433
负责人：
Professor Dr.-Ing. Christoph Egbers
金额：
--
依托单位：
Leibniz-Institut für Astrophysik Potsdam (AIP)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/251213433?language=en
关键词：
Angular momentum transport stratified Taylor

项目摘要

Understanding the mechanisms that can result in an outward angular momentum transport is the central problem of planet formation, particularly in the theory of accretion disks. When a planet forms in a disk, angular momentum has to be carried away from the planet otherwise its rotation speed would be far too large. Only turbulence can achieve such a large angular momentum transport. For disks coupled to a magnetic field the Magneto Rotational Instability (MRI) leads to Magneto Hydrodynamic Turbulence and an associated momentum transport. However, accretion disks can be turbulent even in the absence of a magnetic field, e.g. in regions where the ionization fraction is low. In such regions, the disk cannot be unstable due to MRI and it is an important question to ask whether other instabilities can excite turbulence there. Among other candidates the Strato Rotational Instability (SRI) has attracted attention in recent years. The SRI is a purely hydrodynamic instability and much insight can be obtained from particularly designed laboratory experiments and numerical simulations in an axially-stratified Taylor-Couette (TC) setup. Here the stable axial stratification corresponds with the stratification of the disk while the disk's differential rotation can be approximated by rotating the inner and outer cylinder with different speed. We plan to investigate experimentally and numerically the instability and nonlinear saturation of temperature stratified TC flows in a finite height cylindrical gap and measure/calculate angular-momentum transport in the linear and nonlinear regime. The unstable flow transports angular momentum outwards and will therefore be relevant for astrophysical applications. We will consider different regimes and compare the experimental and numerical findings. In particular, we will measure (i) the transition curve over the full range of numerically feasible Reynolds numbers, (ii) the torque in the stable, unstable, and turbulent regime and we will consider the corresponding spatial patterns, and (iii) the transition to turbulence, the energy spectra in the transition and the turbulent regime, and we want to validate the existence of waves or wave turbulence. The study will give quantitative insight into problems of planet formation and accretion disks.

了解导致角动量向外传输的机制是行星形成的核心问题，特别是在吸积盘理论中。当行星在圆盘中形成时，角动量必须从行星上带走，否则它的旋转速度会太大。只有湍流才能实现如此大的角动量传输。对于耦合到磁场的磁盘磁旋转不稳定性（MRI）导致磁流体动力学湍流和相关的动量输运。然而，吸积盘即使在没有磁场的情况下也可以是湍流的，例如在电离分数低的区域中。在这样的区域中，磁共振成像不会导致盘的不稳定，而其他不稳定性是否会在那里激发湍流是一个重要的问题。在其他候选者中，斯特拉托旋转不稳定性（SRI）近年来引起了人们的注意。SRI是一个纯粹的流体动力学不稳定性和洞察力，可以从特别设计的实验室实验和数值模拟在轴向分层泰勒-库埃特（TC）设置。在这里，稳定的轴向分层对应于磁盘的分层，而磁盘的差动旋转可以近似为旋转的内，外圆柱体以不同的速度。我们计划通过实验和数值模拟研究有限高度圆柱间隙中温度分层TC流的不稳定性和非线性饱和性，并测量/计算线性和非线性区域中的角动量输运。不稳定流向外传输角动量，因此与天体物理学应用有关。我们将考虑不同的制度和比较实验和数值结果。特别是，我们将测量（i）在数值上可行的雷诺数的整个范围内的过渡曲线，（ii）在稳定，不稳定和湍流状态下的扭矩，我们将考虑相应的空间模式，以及（iii）向湍流的过渡，过渡和湍流状态下的能量谱，我们希望验证波或波湍流的存在。这项研究将对行星形成和吸积盘的问题提供定量的了解。