Convection in the presence of a very strong magnetic field

CBET-1232851奥列格·齐卡诺夫密歇根大学？外加恒定磁场可以完全改变导电流体（例如液态金属）的流动的结构和行为，以及流动传输热量和对温度不均匀性作出反应的方式。这种转变在强磁场的情况下尤其引人注目，因为其特征在于哈特曼数的值远大于1。该项目的出发点是发现最近的实验和计算研究的混合对流在管流与横向磁场。研究表明，人们普遍接受的观点是，感应电流的各向异性焦耳耗散会抑制湍流并建立具有稳态速度和温度场的层流，但这种观点并不总是正确的。有一种可能性是，虽然湍流被抑制，浮力引起的不稳定性的扰动均匀沿着磁场线生存，并导致发展的大规模不稳定的相干结构，造成异常的温度波动的特点是高振幅和低主频。这一现象具有潜在的破坏性，目前，人们忽视了锂基冷却和核聚变反应堆增殖毯的影响。如果在包层中出现异常波动，在高热负荷的情况下，其幅度可达几十度。由此产生的不稳定的热应力将导致墙体材料的快速劣化。该提案的目的是从基础科学的角度研究导致异常波动的机制，并评估其在与美国和德国目前开发的毯子的主要组成部分相对应的配置中的可能性。考虑的具体情况包括具有横向温度梯度的水平和垂直管道中的混合对流以及矩形封闭空间中的自然对流。该研究结合了高分辨率三维数值模拟和实验，两者都基于最近开发的方法，首次使强磁场对流能够进行严格的科学分析。该项目是与德国的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非常强（几特斯拉）磁场的液态金属流中检测到的温度的自相矛盾的强烈波动的性质。除了推进基础知识，将特别关注这种波动对核聚变反应堆开发的锂毯的操作和结构完整性的危险，并计划在目前建造的ITER（国际热核聚变实验反应堆）设施进行测试。利用大规模并行计算和新的数值和实验技术，该项目将澄清波动发展的机制，并确定必须避免的毯子组件的配置。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。

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.