基于电子束电离的高超声速磁流体发电机

为了获得高超声速低温来流条件下基于电子束电离的磁流体发电机性能,采用三维低磁雷诺数磁流体动力学五方程模型和简化的电子束电离模型,对等截面分段法拉第型磁流体发电机内的流动进行数值模拟,研究了电离能量花费、磁场强度对发电通道性能的影响,得出了不同电离花费下电离所形成的电子数密度和电导率.研究结果表明,电子束电离低温来流能够产生足够的电导率,当负载系数保持为0.5时,电效率基本保持在0.5 ～0.6之间,电效率大小受磁场强度影响不大,电离能量花费Pion(MW/m3)为0.06,0.6,6,30,300时的电导率σ(S/m)分别为0.28,0.9,3,7,27.当电离能量花费为30MW/m3,能量提取率达到26％,电效率为66％,发电机性能接近最佳,对应的磁场强度为10T.     

有限元三维网格自动生成

讨论了为提高有限元法求解流动问题的精度和效率而寻求自动生成三维网格的方法。给出了利用代数变换、输入极少量区域边界数据即可插值生成三维网格的方法。最后举出了自动生成三维网格的例子。     

1998年5月2日日冕亮度观测图的数值研究

采用数值手段模拟了1998年5月2日日冕亮度观测图.计算模式改进为球坐标系下特殊的二维理想磁流体(MHD)模型,即把(γ,φ)坐标建立在SOHO观测日冕亮度的子午面上,消除了子午面极区的几何奇异性.根据SOHO日冕观测布置磁极子得到初始磁场位形,内边界条件采用自洽的投影特征线边界条件,计算迭代出稳态的多冕流磁场结构,得到了与观测基本一致的亮度图.计算结果表明在太阳表面附近磁场位形对太阳风等离子参数分布起控制作用.     

脉冲等离子体推力器推进剂烧蚀传热计算

运用磁流体动力学的方法,建立脉冲等离子体推力器工作过程模型,展开三维仿真研究,对推进剂的烧蚀传热过程进行分析。通过该模型计算得到的推进剂烧蚀质量和元冲量能够反映出实验结果的大体趋势,同时针对不同电容以及两种不同推力室构型的情况进行了评估。结果显示,推进剂的温度变化波形反映着放电波形的变化波形,影响着推力室等离子体的流动,良好的推进剂表面温度分布更有助于推进剂的喷射过程。     

Determining CME parameters by fitting heliospheric observations: Numerical investigation of the accuracy of the methods

Transients in the heliosphere, including coronal mass ejections (CMEs) and corotating interaction regions can be imaged to large heliocentric distances by heliospheric imagers (HIs), such as the HIs onboard STEREO and SMEI onboard Coriolis. These observations can be analyzed using different techniques to derive the CME speed and direction. In this paper, we use a three-dimensional (3-D) magneto-hydrodynamic (MHD) numerical simulation to investigate one of these methods, the fitting method of  and . Because we use a 3-D simulation, we can determine with great accuracy the CME initial speed, its speed at 1 AU and its average transit speed as well as its size and direction of propagation. We are able to compare the results of the fitting method with the values from the simulation for different viewing angles between the CME direction of propagation and the Sun-spacecraft line. We focus on one simulation of a wide (120–140°) CME, whose initial speed is about 800 km s⁻¹. For this case, we find that the best-fit speed is in good agreement with the speed of the CME at 1 AU, and this, independently of the viewing angle. The fitted direction of propagation is not in good agreement with the viewing angle in the simulation, although smaller viewing angles result in smaller fitted directions. This is due to the extremely wide nature of the ejection. A new fitting method, proposed to take into account the CME width, results in better agreement between fitted and actual directions for directions close to the Sun–Earth line. For other directions, it gives results comparable to the fitting method of Sheeley et al. (1999). The CME deceleration has only a small effect on the fitted direction, resulting in fitted values about 1–4° higher than the actual values.     

磁流体中间激波的相互作用

本文讨论磁流体中间激波的相互作用规律．主要结论：中间激波汇合的产物为后向快简单波、后向慢简单波或慢激波、接触间断、前向慢激波和前向快激波，其中后向波成份和接触间断很弱．当左（右）激波较强时，中国激波碰撞产物为后（前）向快激波、后（前）向慢简单波或慢激波、负（正）切向间断、前（后）向慢简单波和前（后）向快激波．     

磁流体斜激波的汇合

本文讨论磁流体快、慢激波的汇合作用规律,主要结论如下:(1)两个前向快激波汇合之后,形成一更强的前向快激波,尾随一前向慢稀疏波、一正接触间断(后侧密度大于前侧)、一后向慢激波和一后向快稀疏浚。(2)两个前向慢激波汇合之后,形成一更强的前向慢激波,尾随一正接触间断、一后向慢稀疏波和一后向快激波2在前向慢激波前方出现一前向快波,它或为稀疏浚(中、小激波角情况),或为激波(大激波角情况).(3)前向快激波会追上前向慢激波而发生汇合,之后互换位置且强度减弱,尾随一正接触间断和一后向稀疏波对。     

Low frequency turbulence and energy dissipation in the Solar Wind

The possibility to perform in-situ measurements of velocity, magnetic field, density and temperature fluctuations in the Solar Wind has greatly improved our knoweledge of MHD turbulence not only from the point of view of space physics but also from the more general point of view of plasma physics.These fluctuations on the one hand extend over a wide range of frequencies (about 5 decades), a fact which seems to be the signature of turbulent non-linear energy cascade, on the other hand display, mainly in the trailing edge of high speed streams, a number of striking features: (i) a high degree of correlation between magnetic and velocity field fluctuations, (ii) a very low level of fluctuations in mass density and magnetic field intensity, (iii) a considerable anisotropy revealed by minimum variance analysis of the magnetic field correlation tensor. More recently it has been stressed that MHD turbulence in the Solar Wind displays a clear intermittent character.The picture which emerges from the most recent analytical theories and numerical simulations is presented. In particular the observations which give us informations about the dissipation mechanism, which remains yet largely unknown, are discussed.     

磁流体管流准一维模型的数值验证与性能分析

为了快速分析磁流体管流,采用涡轮喷气发动机模型对磁流体管流进行类比分析,引入变截面管流理论和修改过的多变效率表达式,推导了磁流体发电器和加速器的准一维模型,采用二维数值方法验证了准一维模型的可行性,利用该准一维模型对磁流体管流进行了性能分析,结果表明,多变效率的引入使准一维模型更加完整,当负载系数不变时,磁流体装置中的平均马赫数越低,其等熵效率越高。     

Nanoflares and current sheet dissipation

Energy must be continually supplied to the solar corona to maintain both its average temperature and its high energy manifestations. The energy is supplied by photospheric motions and the magnetic field acts both to transmit this energy to the corona and as the furnace in which the energy is stored. The means by which the energy is dissipated and transformed into the actual forms we observe is the activation of current sheets. We conjecture here the properties of such current sheets as derived by both energetical arguments and numerical evidence of the self-organization of a system of currents in a highly turbulent medium. The consequences of the appearance of spatial and temporal intermittency on the different aspects of solar acitvity are also discussed.