倾斜非均匀磁场下导电方管磁流体管流的数值模拟研究

热核聚变反应堆液态金属包层应用中的一个重要问题是液态金属在导电管中流动和强磁场相互作用产生的额外的磁流体动力学压降.这种磁流体动力学压降远远大于普通水力学压降.美国阿贡国家实验室ALEX研究小组,对非均匀磁场下导电管中液态金属磁流体动力学效应进行了实验研究,其实验结果成为液态金属包层数值验证的标准模型之一.液态金属包层在应用中会受到不同方向的磁场作用,本文以ALEX的非均匀磁场下导电方管中液态金属管流实验中的一组参数为基础,保持哈特曼数、雷诺数和壁面电导率不变,采用三维直接数值模拟的方法,研究了外加磁场与侧壁之间的倾角对导电方管内液态金属流动的速度、电流和压降分布的影响.研究结果表明:沿流向相同横截面上的速度、电流以及压力分布均随磁场的倾斜而同向旋转.倾斜磁场均匀段,横截面上的高速区位于平行磁场方向的哈特曼层和平行层交叉位置,压力梯度随磁场倾角的增大先增大后减小.倾斜磁场递减段,在三维磁流体动力学效应作用下,横截面上的高速射流位置向垂直磁场方向偏移.磁场递减段的三维磁流体动力学压降随磁场倾角的增大而增大.随磁场倾斜,截面上的射流峰值逐渐减小,二次流增强,引发层流向湍流的转捩. 

DIRECT NUMERICAL SIMULATION OF MHD FLOW IN CONDUCTING SQUARE DUCTS WITH INCLINED FRINGING MAGNETIC FIELD1)

An essential issue in the application of liquid metal blanks in thermal nuclear fusion reactors is the additional magnetohydrodynamic (MHD) pressure drop caused by the interaction of the liquid metal flow with a strong magnetic field. The additional MHD pressure drop is much higher than hydrodynamic pressure drop. Argonne liquid metal experiment (ALEX) group in Argonne National Laboratory of American studied the MHD effect of Liquid Metal flow in ducts and pipes subjected to a fringing magnetic field by experiments. The experiments were introduced as one of the benchmark cases to test numerical codes for liquid metal blankets. As the liquid metal blankets would be subjected to the magnetic field with different directions, liquid metal flow in a square duct subjected to an inclined fringing magnetic field has been numerically studied in this paper. The model is based on one of the ALEX's experiments. With constant Hartmann number, Reynolds number and wall conductance ratio, the effects of the angle between the magnetic field and the side wall on the velocity, the electric current, and the pressure distribution have been investigated using three-dimensional direct numerical simulation method. The results show that the distribution of the velocity, the electric current and the pressure on the cross section rotates with the increase of the inclination angle of the magnetic field. In the uniform part of the inclined magnetic field, the velocity jets located at the junction corners of the Hartmann layer and the side layer which are parallel to the external magnetic field. The pressure gradient in the part of the uniform magnetic field increases firstly and decreases with the increase of the inclination angle of the magnetic field. In the decreasing part of the inclined magnetic field, the high-speed velocity jet is transferred to another pair of corners due to the three-dimensional MHD effect along the streamwise direction. The three-dimensional MHD pressure drop at the cross-section of the duct increases with the increase of the inclination angle of the magnetic field. Furthermore, the maximum value of the velocity jets decreases, the second flow increases and the laminar-turbulent transition of the duct flow occurs.