Effect of shear and magnetic field on the heat-transfer efficiency of convection in rotating spherical shells
Effect of shear and magnetic field on the heat-transfer efficiency of convection in rotating spherical shells
复制标题
剪切和磁场对旋转球壳内对流换热效率的影响
DOI：
10.1093/gji/ggv506
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发表时间：
2016
影响因子：
2.8
通讯作者：
Reiners
中科院分区：
文献类型：
--
作者：
Gastine;Christensen;Duarte;L. D. V;Reiners
我们研究旋转的热对流球壳流动的原型在类地行星，气体行星或恒星的核心。我们的分析基础上的一组约450直接数值模拟的（磁）流体动力学方程下的Boussinesq近似。埃克曼数的范围从10− 3到10−5。对流的超临界性在某些模型中达到约1000。四组模拟被认为是：非磁模拟和发电机模拟与自由滑动或无滑移流动边界条件。具有自由滑移边界的非磁性设置产生最强的带状流。无滑移流动边界条件的非磁性模拟和自由滑移边界的自洽发电机都大大减少了区域流动。剪切的抑制导致传热效率的显著增加，在某些情况下增加3倍。只要对流受到旋转的显著影响，就会发生这种效率提高。在较高的对流驱动下，传热效率趋向于经典的非旋转Rayleigh-Bénard系统。对外边界热流纬向分布的分析表明，在赤道地区，切变对抑制热传递是最有效的。不同厚度对流区的模拟结果表明，带状流在较厚的壳层中变得能量较低，因此，它们对传热效率的影响降低。此外，我们还探讨了磁场对对流中非带状流动分量的影响。为此，我们比较了无滑非磁性的情况下，无滑发电机模拟的传热效率。我们发现，在E = 10− 5的磁场显著影响对流和传热效率的最大增益约为30%（与非磁性的情况相比）的埃尔萨瑟数约为3。我们的分析促使我们推测，在E = 10− 5的发电机中，极区的对流可能处于“磁转”状态。
We study rotating thermal convection in spherical shells as prototype for flow in the cores of terrestrial planets, gas planets or in stars. We base our analysis on a set of about 450 direct numerical simulations of the (magneto)hydrodynamic equations under the Boussinesq approximation. The Ekman number ranges from 10−3to 10−5. The supercriticality of the convection reaches about 1000 in some models. Four sets of simulations are considered: non-magnetic simulations and dynamo simulations with either free-slip or no-slip flow boundary conditions. The non-magnetic setup with free-slip boundaries generates the strongest zonal flows. Both non-magnetic simulations with no-slip flow boundary conditions and self-consistent dynamos with free-slip boundaries have drastically reduced zonal-flows. Suppression of shear leads to a substantial gain in heat-transfer efficiency, increasing by a factor of 3 in some cases. Such efficiency enhancement occurs as long as the convection is significantly influenced by rotation. At higher convective driving the heat-transfer efficiency tends towards that of the classical non-rotating Rayleigh–Bénard system. Analysis of the latitudinal distribution of heat flow at the outer boundary reveals that the shear is most effective at suppressing heat-transfer in the equatorial regions. Simulations with convection zones of different thickness show that the zonal flows become less energetic in thicker shells, and, therefore, their effect on heat-transfer efficiency decreases. Furthermore, we explore the influence of the magnetic field on thenon-zonalflow components of the convection. For this we compare the heat-transfer efficiency of no-slip non-magnetic cases with that of the no-slip dynamo simulations. We find that atE= 10−5magnetic field significantly affects the convection and a maximum gain of about 30 per cent (as compared to the non-magnetic case) in heat-transfer efficiency is obtained for an Elsasser number of about 3. Our analysis motivates us to speculate that convection in the polar regions in dynamos atE= 10−5is probably in a ‘magnetostrophic’ regime.