Numerical Modelling Point-to-Plane of Negative Corona Discharge in N_2 Under Non-Uniform Electric Field

The paper presents a simulation model of the negative corona discharge in N2 under various pressures. The simulated discharge is of a negative point-to-plane mass type, with an inter-electrode separation distance of 20 mm and a symmetry about the axis of discharge. This simulation investigates the behavior of the neutral density and temperature for different pressures in the range of 0.1-10.0 bar. The spatial and temporal evolution of the neutral gas is analyzed based upon the equations of continuity, momentum and energy in a two-dimensional cylindrical geometry model. For that geometry of the system, the FCT （Flux Corrected Transport） technique was adopted. The results show that the pressure plays a significant role of the neutrals dynamics.

Numerical studies of the Kelvin-Hemholtz instability in a coronal jet

Kelvin-Hemholtz（K-H）instability in a coronal EUV jet is studied via 2.5D MHD numerical simulations.The jet results from magnetic reconnection due to the interaction of the newly emerging magnetic field and the pre-existing magnetic field in the corona.Our results show that the Alfv e′n Mach number along the jet is about 5–14 just before the instability occurs,and it is even higher than 14 at some local areas.During the K-H instability process,several vortex-like plasma blobs with high temperature and high density appear along the jet,and magnetic fields have also been rolled up and the magnetic configuration including anti-parallel magnetic fields forms,which leads to magnetic reconnection at many X-points and current sheet fragments inside the vortex-like blob.After magnetic islands appear inside the main current sheet,the total kinetic energy of the reconnection outflows decreases,and cannot support the formation of the vortex-like blob along the jet any longer,then the K-H instability eventually disappears.We also present the results about how the guide field and flux emerging speed affect the K-H instability.We find that a strong guide field inhibits shock formation in the reconnecting upward outflow regions but helps secondary magnetic islands appear earlier in the main current sheet,and then apparently suppresses the K-H instability.As the speed of the emerging magnetic field decreases,the K-H instability appears later,the highest temperature inside the vortex blob gets lower and the vortex structure gets smaller.

Space Charge Transient Kinetic Characteristics in DC Air Corona Discharge at Atmospheric Pressure

Investigating the corona mechanism plays a key role in enhancing the performance of electrical insulation systems. Numerical simulation offers a better understanding of the physical characteristics of air corona discharges. Using a two-dimensional axisymmetrical kinetics model, into which the photoionization effect is incorporated, the DC air corona discharge at atmosphere pressure is studied. The plasma model is based on a self-consistent, multi-component, and con- tinuum description of the air discharge, which is comprised of 12 species and 22 reactions. The discharge voltage-current characteristic predicted by the model is found to be in quite good agree- ment with experimental measurements. The behavior of the electronic avalanche progress is Mso described. 0＋ and N＋ are the dominant positive ions, and the values of 0- and 02 densities are much smaller than that of the electron. The electron and positive ion have a low-density thin layer near the anode, which is a result of the surface reaction and absorption effect of the electrode. As time progresses, the electric field increases and extends along the cathode surface, whereas the cathode fall shrinks after the corona discharge hits the cathode; thus, in the cathode sheath, the electron temperature increases and the position of its peak approaches to the cathode. The present computational model contributes to the understanding of this physical mechanism, and suggests ways to improve the electrical insulation system.

Study on the interaction mechanism of double-blade corona discharge with a large discharge gap

Multi-source corona discharge is a commonly used method to generate more charged particles,but the interaction mechanism between multiple discharge sources,which largely determines the overall discharge effect,has still not been studied much.In this work,a large-space hybrid model based on a hydrodynamic model and ion-transport model is adopted to study the interaction mechanism between discharge sources.Specifically,the effects of the number of electrodes,voltage level,and electrode spacing on the discharge characteristics are studied by taking a double-blade electrode as an example.The calculation results show that,when multiple discharge electrodes operate simultaneously,the superimposed electric field includes multiple components from the electrodes,making the ion distribution and current different from that under a single-blade electrode.The larger the distance between discharge electrodes,the weaker the interaction.When the electrode spacing d is larger than 4 cm,the interaction can be ignored.The results can guide the design of large discharge gap array electrodes to achieve efficient discharge.

Multi-point discharge model: study on corona discharge of double-ended needle in large space

Corona discharge, as a common means to obtain non-equilibrium plasma, can generally obtain high-concentration plasma by increasing discharge points to meet production needs. However,the existing numerical simulation models used to study multi-point corona discharge are all calculations of small-scale space models, which cannot obtain the distribution characteristics of plasma in large space. Based on our previous research, this paper proposes a hybrid model for studying the distribution of multi-point discharge plasma in large-scale spaces, which divides the computational domain and computes separately with the hydrodynamic model and the ion mobility model. The simulation results are verified by a needle–ball electrode device. Firstly, the electric field distribution and plasma distribution of the needle electrodes with single tip and double tips are compared and discussed. Secondly, the plasma distribution of the needle electrode with the double tip at different voltages is investigated. Both computational and experimental results indicate that the charged particle concentration and current of the needle electrode with double tips are both twice as high as those of the needle electrode with a single tip. This model can extend the computational area of the multi-point corona discharge finite element model to the sub-meter(25 cm) or meter level, which provides an effective means to study the plasma distribution generated by multiple discharge points in large-scale space.

Numerical simulation on ionic wind in circular channels

Ionic wind induced by direct-current corona discharge has attracted considerable interest because of its low energy consumption, low noise emission, flexible designs, and lack of moving parts. The purpose of this study is to investigate the configuration parameters to improve the velocity of the ionic wind. Accordingly, this study develops a three-dimensional(3 D) model of circular tube with multi-needle-to-mesh electrode configurations, in this model, the influences of various parameters were explored,such as the mesh gap, the distribution of needle electrodes, the number of needle electrodes,and the radius of the circular channel. The numerical research results showed that the mesh gap, the distribution of needle electrodes, and the radius of the circular tube significantly affected the velocity of the ionic wind. When mesh gap is 12 mm,which indicates that there is an optimal mesh gap which can enhance the velocity of the ionic wind. What is more, changing the distribution of needle electrodes and increasing the number of needle electrodes can effectively improve the velocity of the ionic wind, the optimum distribution α of needle electrodes is 0.7–0.9, which greatly increase the velocity of the ionic wind. However, for multi-needle-to-mesh structure, the improvement of the radius of the circular channel is conducive to enhance the velocity and improve the velocity distribution.

Numerical research on the interaction between coronal mass ejection and streamer

By proposing a two-dimensional triggering model with concentrically circular closed magnetic field line structure,numerical research is made on the asymmetric propagation feature of coronal mass ejection (CME) in two cases emerging at the solar northern latitudes 10° and 45° respectively.The numerical results can qualitatively explain some features of CME event observed by the spacecraft SOHO and show that:(i) In these two cases,the triggering model can initiate CME with an asymmetric closed magnetic field structure.(ii) Closed magnetic structure of CME event will keep deflecting to the current sheet when it propagates away from the sun and this deflecting effect mostly happens within tens of solar radii before CME travels finally along the current sheet.(iii) The triggering model emerging at different locations can introduce CME events with different magnetic shapes.This shape happens to be circular and crescent when the triggering model emerges at the northern latitudes 10° and 45°,respectively.

类环状CMEs形成的数值模拟

对于不同磁场强度冕旒位形中，热驱动日冕瞬变的数值模拟表明，β（＝2μ0P／B2）值的大小对瞬变的形态有重要的控制作用，只有β较小（如太阳表面赤道处β0等于0．25）时才可重现典型环状CMEs观测形态：足部出现在开场与闭场的交界面上，在纬向基本不动；CMEs顶部物质变化在传播过程中沿电流片两侧移动，使顶部物质密度变化比两侧小．

微尺度下场致发射对电晕放电的影响机理

场致离子化微电晕器件基于一维纳米材料的电场增强效应,可产生大气压非平衡微等离子体,适用于气体检测以及生物医疗等领域,具有响应快、低功耗等特点。但微尺度下的电晕放电属于局部自持的低能放电,其场致发射的作用及影响机制尚不清晰。因此文章基于流体-化学混合模型框架,融合F-N发射模型,建立了常温常压N2-O2混合气体的二维微电晕放电模型。通过与无场致发射放电模型对比,探索不同间距下场致发射对放电动态过程的影响,发现针-板间距减至15μm时,两种模型放电过程差异很小,表明放电以二次电子发射机制为主导,当间距减至10μm时,两种模型的放电强度相差近1倍,场致发射的作用及影响不可忽略;通过进一步对电子密度分布、空间电场分布、电流密度等参量进行动态分析,发现场致发射、空间碰撞电离反应和离子轰击二次电子发射之间存在链锁影响规律。

风沙条件下导线电晕特性的模拟试验系统设计

为了对西北地区高海拔风沙天气条件下的导线电晕特性系统地展开研究,并克服恶劣的气候环境给研究工作带来的困难,通过对西北当地风沙环境调研,确定基本风沙参数;结合超高压电晕笼,通过理论分析计算、采用Fluent软件的k-ε湍流模型对气固两相流进行数值模拟,计算出能够满足电磁学和流体力学两方面性能基本要求的风管系统;再结合一系列电晕特性测量系统,设计出风沙条件下导线电晕特性的模拟试验系统。该系统在满足科学可行的前提下,具有高可控性,同时保证尽可能地贴近实际情况;研究成果可为进一步开展高海拔风沙气候条件下的导线电晕特性研究奠定基础,同时也为风沙物理学的研究提供参考。

无振荡、无自由参数格式在三维太阳风流动数值模拟中的应用

从快速、有效地进行空间天气数值预报的需要出发，针对1998年5月份行星际太阳风暴事件，采用全三维流体力学（HD）模型进行数值试验，考察了无振荡、无自由参数（NND）格式在三维太阳风流动数值模拟中的应用。计算中内边界的密度分布由观测K日冕数据来确定，由此得到的源表面密度分布具有和源表面电流片相似的结构数值试验表明：虽然该格式不需要加入人工粘性，但是具有很好的计算稳定性，在扰动计算时激波间断耗散小，在三维任何方向上间断所占的网格数比较少，没有数值色散现象．

电晕放电电流体状态实验研究与数值模拟

为了分析电晕放电过程中电流体的形成过程及放电空间的流体分布状态,采用实验分析和数值模拟相结合的方法进行了实验研究。先在分析线板电晕放电伏安特性及极板处离子风分布变化的基础上确立了离子风速v与放电电压U之间的关系为v=(0.126-0.0217U+9.418×10-4U2)×23.3,然后建立线板放电二维模型并在流场分析平台Fluent软件上利用动力风代替离子风的方法,根据放电电压与离子风速之间的关系,模拟不同电压下放电通道内的电流体的状态。模拟显示的不同电压下离子风在极板处的衰减结果与相同条件下该处的实验值具有很好的符合度,从而证明简化的数值模拟方法及确立的电压和离子风速关系的正确性。采取的实验方法及数值模拟方法不仅简化了复杂的电流体流场问题,其结论也为除尘器的设计提供了必要的理论支持。

棒-板电极直流负电晕放电脉冲过程中的电子特性研究

为了揭示负电晕放电过程的电子特性,本文对棒-板间距3.3mm,施加电压-5.0kV,大气压强1.0atm(1atm=101 325Pa),环境温度300K时的空气(N_2:O_2=4:1)负电晕放电微观过程进行数值计算,该过程主要通过求解改进的电子连续性方程、电子平均能量方程、重粒子连续性方程和泊松方程实现,计算结果表明单次脉冲的波形特性和实验结果符合较好。文中选取单次脉冲持续周期内的6个典型时间点对负电晕放电过程中的电子特性进行详细描述,结果表明:电子温度的最大值出现在场致电离区,随着放电时间的发展由阴极向阳极移动,温度值也随之减小。电子密度在阴极鞘内近似为0,在阴极鞘外层具有最大值,随着放电时间的增加,电子分布区域由阴极向阳极扩展,并且棒-板间隙内的电子密度逐渐增加。R_1和R_2分别为与N_2和O_2有关的碰撞电离反应,是电子增殖的主要过程,在整个放电过程中R_1和R_2的反应速率几乎保持一致;R_(17)是涉及N_2、N_2^+和电子的三体复合反应,在电子消散过程中占绝对优势。

两冕流间CME事件数值模拟的改进

通过偶极子场和六极子场适当叠加,改进猜解磁场,使猜解磁场在太阳南北极符号相反,然后采用理想磁流体力学方程组(MHD),由猜解磁场与太阳风流动相互作用计算出稳态自洽解,得到定性上与观测比较接近的具有两个冕流的背景结构.在两个冕流间采用具有同心圆磁场位形的触发模型触发CME事件,研究CME的日冕传播特征.模拟结果表明,CME被约束在两冕流间传播,CME闭磁场位形和磁云横截面磁场位形相似,可以解释1 AU处观测磁云的部分特征;在CME附近,存在压力和Lorentz力起主要作用的区域,这可以为分析1 AU处CME事件的观测数据提供帮助.

电晕耦合无声放电结构电极配置数值模拟

提出了一种电晕耦合无声放电结构,通过对线-板式电晕耦合无声放电结构静电场进行数值模拟,得出了不同线-板电极配置下的电场分布,结合流光形成、发展和传播所需的静电场条件,分析了电极配置。结果表明,对于一定的放电电压和线-板间距,存在一个较优的线电极直径,使之既满足于电晕放电的起晕,又满足于流光放电的发生、发展及稳定传播。对于一定的线-板间距,线-线间距存在一个有效范围。

等离子体射流在磁场作用下的特性模拟

磁流体发电是一种高效、低污染的发电技术。相对于其他发电方式,磁流体发电具有输出功率大、结构紧凑的优点,在高功率电源应用领域有不可替代的性能优势。文中提出采用非平衡等离子体射流的方式产生等离子体,进行磁流体发电的设想。通过数值模拟研究了等离子体射流在横向磁场作用下的特性,并通过试验对模型计算结果进行了验证。模拟研究说明横向磁场对等离子体射流有阻滞作用,在没有外电流回路的情况下,射流气体的动能转化为热,随外加磁场强度的增加,阻滞作用越强,速度减慢越明显;等离子体射流在磁场作用下电流密度主要集中在射流出口附近,并随着外加磁场强度增大而增大。

荷电喷雾电晕电极诱导电场数值计算与分析

为深入研究电晕荷电喷雾产生电场的分布情况,针对电晕荷电喷雾中常用的多针组合式电极,采用电荷模拟法,运用matlab软件编程,对电极诱导电场进行数值计算,得出了电场中任意点的电势、场强值及其分布图。通过计算分析发现,电晕放电产生的静电场是极不均匀的;场强由电极结构参数-极径、电极尖端曲率半径、电极电压、针状电极的个数以及电极环中心距地面的垂直高度决定;雾滴从喷嘴到靶标的输运过程中,电晕电极产生的电场仅在输运初始阶段对雾滴的运动起主导作用。

具有不对称结构的电晕放电模型建立及应用

详细研究尖端电晕放电特征对深入探讨地闪连接过程(或称为闪击过程)以及先导发展和传播机制是极为重要的。在实际雷暴云下,地面尖端发生电晕放电时,通常均有风的存在(导致电晕扩散不对称),且地面通常具有多个尖端共存(电晕放电尖端的不对称性),在这些实际情况下,电晕离子在扩散过程中是很难对称分布的。然而由于现有的雷暴云下的电晕扩散模型多为一维模型或二维轴对称模型,对于不对称结构无法模拟,因此在模拟分析实际问题时具有一定的局限性。为了更好地模拟符合实际雷暴云环境下的电晕放电过程,建立了二维直角坐标系下的电晕放电模型。通过与实际观测和已有模式结果的对比,验证了本模式的模拟能力。并初步模拟了具有风或多针存在时的电晕放电过程,进一步证明了本模式的实际价值。

1998年5月日冕三维结构的数值模拟

采用三维理想磁流体力学（ＭＨＤ）模式，内边界条件把二维投影特征线边界方法推广应用到三维计算，有效地稳定了数值计算并保证稳态解的自洽性；初始猜解磁场由１９３５卡林顿周光球磁场观测数据得到，这样计算得到的１９９８年５月份期间日冕三维结构比较符合实际．计算结果表明：（１）计算得到的源表面非径向磁场量值在磁中性线附近不超过２μＴ，表明源表面磁场基本径向．（２）模拟得到的源表面径向磁场量值除了在磁中性线附近的区域外变化不大，这和观测一致．（３）由源表面磁场按平方反比的规律计算出 １ ＡＵ处磁场量值更接近观测值．（４）计算得到的日冕结构和观测定性一致．三维数值模拟结果还表明，日冕的三维大尺度背景结构主要是由磁场决定的，在闭磁场处或者电流片附近，太阳风的密度高，速度低；在开场区，太阳风的密度低，速度高．

无电晕式高温高压静电除尘器的数值模拟

基于实验研究结果,对无电晕式高温高压静电除尘器的阴极电子发射、粉尘荷电、浓度扩散、烟气流动、尘粒捕集等过程进行了数值模拟,从理论上分析讨论了温度、压力、电压、流速、含尘浓度、比电阻以及粒径等因素对除尘效率的影响,计算结果与实验结果基本吻合。研究发现,与传统的电晕式静电除尘器不同,无电晕式静电除尘器可以在较高含尘浓度和较低电压下正常工作,且特别适用于高温(高压)烟气的除尘。