Convection in the presence of a very strong magnetic field

CBET-1232851Oleg zikanov密歇根大学？施加恒定磁场可以完全改变导电流体（如液态金属）流动的结构和行为，以及流动传递热量和对温度不均匀性的反应方式。在强磁场的情况下，这种转变尤其显著，其特点是哈特曼数的值远远大于1。本课题的出发点是对近年来在横向磁场作用下管道流动中混合对流的实验和计算研究的发现。结果表明，普遍认为的感应电流的各向异性焦耳耗散导致湍流抑制和建立具有稳态速度和温度场的层流的观点并不总是正确的。有一种可能性是，当湍流被抑制时，浮力引起的沿磁力线均匀扰动的不稳定性仍然存在，并导致大规模非定常相干结构的发展，导致以高振幅和低主导频率为特征的异常温度波动。这种现象具有潜在的破坏性，目前，人们忽视了对核聚变反应堆的锂基冷却和繁殖毯的影响。在高热负荷的情况下，如果包层出现异常波动，其幅度可达几十度。由此产生的非定常热应力将导致壁材的迅速劣化。该提案的目的是从基础科学的角度调查导致异常波动的机制，并评估其在与目前在美国和德国开发的毯子的主要成分相对应的配置中的可能性。要考虑的具体情况包括水平和垂直管道中具有横向温度梯度的混合对流和矩形外壳中的自然对流。本研究将高分辨率三维数值模拟与实验相结合，采用最新发展的方法，首次使强磁场对流可以进行严格的科学分析。该项目是与德国伊尔梅瑙理工大学和卡尔斯鲁厄理工学院合作进行的。该项目将探索最近在受到很强（几个特斯拉）磁场影响的液态金属流动中检测到的矛盾的强烈温度波动的本质。除了提高基本知识外，还将特别注意这种波动对为核聚变反应堆开发并计划在目前建造的国际热核实验反应堆（ITER）设施进行测试的锂包层的操作和结构完整性的危险。利用大规模并行计算和新颖的数值和实验技术，该项目将阐明波动发展的机制，并确定必须避免的包层组件的配置。该项目将与德国的两所大学进行国际合作。它将为一名研究生和几名本科生提供教育机会和接触国际研究环境的机会。

CBET-1232851Oleg ZikanovUniversity of Michigan ? DearbornAn applied constant magnetic field can completely change the structure and behavior of a flow of an electrically conducting fluid, such as a liquid metal, and the way in which the flow transports heat and reacts to temperature non-uniformities. The transformation is especially dramatic in the case of strong magnetic fields, as characterized by the values of the Hartmann number much larger than one. The starting point of the project is the finding of the recent experimental and computational studies of mixed convection in the pipe flow with transverse magnetic field. It has been demonstrated that the commonly accepted view that the anisotropic Joule dissipation of the induced electric currents leads to suppression of turbulence and establishing of a laminar flow with steady-state velocity and temperature fields is not always correct. There is a possibility that, while turbulence is suppressed, the buoyancy-induced instability to the perturbations uniform along the magnetic field lines survives and leads to development of large-scale unsteady coherent structures that cause anomalous temperature fluctuations characterized by high amplitudes and low dominant frequencies. The phenomenon has potentially disruptive and, at the moment, ignored implications for the Li-based cooling and breeding blankets for the nuclear fusion reactors. Should the anomalous fluctuations develop in the blanket, their amplitude can, in the presence of high thermal load, reach several tens of degrees. The resulting unsteady thermal stresses will cause rapid deterioration of the wall material. The objective of the proposal is to investigate the mechanisms leading to the anomalous fluctuations from the fundamental science perspective and to assess their likelihood in the configurations corresponding to the principal components of the blankets currently developed in the U.S. and Germany. The specific cases to be considered include the mixed convection in horizontal and vertical ducts with transverse temperature gradient and natural convection in rectangular enclosures. The research combines the high-resolution three-dimensional numerical simulations and experiments, both based on the recently developed methods that, for the first time, make the convection with strong magnetic field amenable to rigorous scientific analysis. The project is conducted in collaboration with the Ilmenau University of Technology and Karlsruhe Institute of Technology in Germany. The project will explore the nature of the paradoxical strong fluctuations of temperature recently detected in flows of liquid metals subjected to very strong (several Tesla) magnetic fields. In addition to advancing the basic knowledge, particular attention will be paid to the danger of such fluctuations for the operation and structural integrity of the lithium blankets developed for nuclear fusion reactors and planned for testing at the currently constructed ITER (International Thermonuclear Experimental Reactor) facility. Using the massively parallel computations and novel numerical and experimental techniques, the project will clarify the mechanisms, by which the fluctuations develop, and identify the configurations of the blanket components that have to be avoided. The project will be undertaken as international collaboration with two universities in Germany. It will provide educational opportunities and exposure to international research environment to one graduate and several undergraduate students.