行波管三维非线性计算机模拟的改进

 采用宏粒子模型计算空间电荷力,导出行波管三维大讯号工作方程组,开发出Visual C++数值分析软件。随后进行计算机模拟,提出将三维空间电荷力处理为二维,大大节省了计算时间,数值结果与三维计算吻合很好。     

干气密封三维微间隙流场数值模拟

采用三维流动求解器CFD-ACE ,以空气作为工作介质,对干气密封不同工况下的内部微间隙三维流场进行了数值模拟,得到了流场的压力分布及其产生的开启力,通过与文献中试验结果的比较和分析,三维流场的计算结果与文献中试验结果吻合较好.在考虑气体的可压缩性的情况下,直接求解N-S方程可对干气密封微间隙内的三维流场进行正确的描述.     

改进特征有限元法求解高度非线性的海水入侵问题

提出了用改进特征有限元法求解高度非线性的海水侵问题，以克服在求解这一问题的碰到的数值弥散和振荡困难，所求的三维海水入侵数学模型以交换阳离子Ｎａ＾＋，Ｃａ＾２＋作为模拟因子，考虑了水－岩间的阳离子交换作用，将模型计算结果与观测结果进行了对比验证。     

低速压气机中静叶Clocking效应的二维和三维数值模拟与实验结果验证

本文采用二维和三维非定常数值模拟的方法研究了低速压气机的静叶时宁效应。与实验结果进行对比分析后发现,二维和三维数值模拟均捕捉到了较明显的静叶Clocking效应:二维计算得到的效率变化幅度为0.51%,三维计算的结果为0.42%,均低于实验结果(1.1%)。二维计算很好的验证了Clocking效率曲线的走势,但三维计算的结果则存在相位上的偏差。文中应用负射流理论解释三维计算中较大的数值粘性带来的尾迹偏移现象。     

涡轮动叶冷却结构设计方法Ⅲ:气热耦合计算

三维气热耦合数值模拟是涡轮叶片冷却结构详细设计中应用的热分析方法。三维气热耦合数值模拟的计算域实体模型建立借助于参数化方法,模型包括冷却结构尽可能多的细节、并保证足够高的模型精度。网格生成时,流体域采用结构化网格,并且需要在换热壁面上根据湍流模型的要求进行加密。将管网计算结果与三维数值模拟结果进行对比,发现管网计算的精度有限,而气热耦合计算方法能够捕捉更多流动换热现象,计算结果相对可信。对单个冷却结构方案进行三维数值计算的周期为5～15天,基本满足工程设计要求。     

对旋轴流水轮机的非定常数值模拟研究

为了研究采用对旋转轮的新型轴流式水轮机的非定常性能,应用三维非定常数值计算方法,对该新型水轮机进行了数值模拟研究.数值计算中,采用了全三维全流道的数值计算方法,基于DES(Detached Eddy Simulation)方法获得了对旋轴流水轮机的非定常流场和能量性能.计算结果显示,该新型水轮机在一个转动周期的不同时刻,其内部流场存在显著的非定常特性.     

应用高分辨率迎风格式精确分析透平叶栅三维湍流流场

应用高收敛率、高精度和高分辨率的数值计算方法,通过求解全三维可压缩雷诺平均的Navier－Stokes方程和q－ω低雷诺数双方程湍流模型,数值模拟了VKI跨音速叶栅内的三维流场,对叶棚内的三维流动结构进行了细致的分析。计算表明,本文采用的计算方法可以精确模拟叶轮机械内部的复杂流动。     

毛细力比对环形液池内耦合热-溶质对流的影响

为了了解毛细力比R_σ对耦合热溶质毛细对流的影响,对深宽比为0.15的环形浅液池内双组分溶液耦合热-溶质毛细对流进行了三维数值模拟。液池内、外壁分别维持恒定温度和浓度,工质为甲苯/正己烷混合溶液,Prandtl数为5.54,Lewis数为25.8。结果表明,当热毛细Reynolds(ReT)数较小时,耦合热-溶质毛细对流为三维稳态流动,当ReT数超过临界值后,流动将转变为三维周期性振荡流动;在计算范围内(-1≤R_σ≤0),随着毛细力比的增加,流动失稳的临界Re_T数会逐渐减小。     

带间断性矩肋的平行平板通道中三维流动与换热的数值模拟

1数学描述与计算方法周期性变化的几何结构是广泛应用的一种强化换热形式＊‘］。文献中有关的数值研究多限于二维清形，三维的研究相对较少。本文针对沿流向周期性布置矩肋的平行平板通道，对层流周期性充分发展的流动与换热进行了三维数值模拟。计算单元如图1所示。对于不可压缩流体，忽略体积力时的控制方程为：图1矩助通道计算单元表1式（l）中各乡变量的含义式中d取不同值的对应关系见表1。设通道几何周期长度为S，则对充分发展状态的计算单元进出边界有如下关系：据文献＊，周期性充分发展流动的压力可以分解为两部分：式中o为一个周…     

循环流化床提升管内气固流动的三维数值模拟研究

采用双流体模型结合基于流动结构的EMMS曳力模型,对一方形截面循环流化床提升管在同一操作气速、不同固体流率下的两种工况进行了三维数值模拟研究。得到了提升管内气固流动的三维浓度分布,并对比了二维模拟的结果。验证了EMMS曳力模型对于快速流态化三维模拟的适用性。     

Three-Dimensional Numerical Analysis for Millimeter Wave TWTs

Based on Macro–particle model, the electron beam can be subdivided into 3D Macro–particles to calculate space–charge forces and 3D large–signal working equations are obtained. Finally, the numerical results for a uniform magnetic focusing field are given.     

Suppression of third-order intermodulation in a klystron by third-order injection

The first observations and measurements are reported on suppression of the third-order intermodulation (IM3) product arising from nonlinear mixing of two drive frequencies in a klystron, by externally injecting a wave at the IM3 product frequency. Optimum amplitude and phase of the injected wave for maximum suppression are examined. Results indicate that suppression of the IM3 product by as much as 30 dB can be achieved. Experimental results compare favorably with predictions of a 1D simulation code that takes into account all kinematical and dynamical effects including charge overtaking and space charge forces.     

Adiabatic theory of particle trapping due to Coulomb crossing of one-dimensional betatron resonance

In the presence of space charge forces, synchrotron oscillations result in periodic modulation of the space charge tune shift, periodic crossing of betatron resonances, and particle trapping in resonance islands. The trapping effect for one-dimensional resonance is considered using classical perturbation theory and the “frozen core” approach to calculation of space charge forces. The beam losses and emittance growth are analyzed for arbitrary order resonance; the numerical results are given for the third-order resonance. The text was submitted by the authors in English.     

Numerical simulation for space charge dominated beam transport

To simulate the intense bunched beam transport, a computer program LEADS-3D has been developed. The particle trajectories are analysed with the Lie algebraic method. The third order approximation of the trajectory solutions is made with space charge forces off, and the second order approximation is made with space charge forces on. The particle distribution in the 3D ellipsoid is uniform or Gaussian. Most of the conventional beam optical elements are incorporated in the code. The optimization procedures are provided to fit the beam lines to satisfy the given optical conditions.     

强流AVF型迴旋加速器中的空间电荷效应和束晕

详细推导了AVF型迴旋加速器中束团粒子在曲线坐标系中的动力学方程(考虑和不考虑空间电荷相互作用力两种情况).在假定动力学方程中各参数值的前提条件下,用Lunge-Kutta方法对考虑空间电荷时的动力学方程进行了数值计算.结果表明,束晕的形成和发展同样也是强流迴旋加速器中束流损失的一个主要原因.但束晕形成的机制不同于直线加速器的情况,它不是由共振和混沌引起,而是由于粒子的排斥运动和束团内粒子的涡流运动引起的.     

Effects of the Space Charge Forces and the Beam Halo in an AVF Cyclotron with Intense Beam Currents

The equations of motion of particles in an AVF cyclotron in a curvilinear coordinate system are derived for the cases with and without space charge forces. Assuming a set of the parameter values in the equations, numerical calculations are carried out by using Lunge-Kutta methods in the case with space charge forces. The results show that the formation of the beam halo is also a main reason of the beam losses, but the mechanism here is different from that in a linear accelerator. It is not given rise by resonance and chaos but the outward repellent motion and the vortex motion of the particles in the bunch.     

Space charge effects on radiative ultrashort laser-plasma interactions: Relativistic fluid model

Ultrashort laser-gas interaction is a promising candidate for the intense broad band far-infrared radiation in which the gas ionization and the resultant plasma formation occur consequently. The electron current produced in the process is the most important influential parameter which affects the far-infrared radiation generation. Although the interacting forces of the process are the space charge electric and the laser electromagnetic forces, the effect of the former one, has not been investigated on the gas-plasma THz generation. It is noteworthy that the space charge electric force, due to its effect on the electron distribution, has potential influence on the produced electron current and its consequent emission. Here, a 2D relativistic fluid model is presented in which the ions and the resultant space charge field are incorporated. The model investigates the air ionization, electron-ion plasma formation, and the system's evolution, spatiotemporally. Moreover, as the model is based on the transient electron current, as the source for the electromagnetic pulse radiation, it gives the temporal profile of the radiated field in which the space charge effects are observable. Our results show that the space charge field affects the electron velocity and its resultant current. Therefore, the temporal profiles and amplitudes of the radiated field components are affected and their resemblance to the experimental data is enhanced. The results indicate that the amplitude of the radiated field increases in the presence of the space charge field. In addition, it is shown that the space charge effects become more pronounced with the laser intensity.     

Numerical simulation of the electrostatic powder coating process with a corona spray gun

In this paper results of investigations are described aiming to numerically simulate the electrostatic powder coating process using an extended commercial computational fluid dynamics (CFD) code. The fully three-dimensional turbulent flow was calculated. Based on the Lagrangian approach the trajectories of the powder particles were modelled considering electric and aerodynamic forces. In the calculations of the particle propagation both the particle size distribution and the particle charge distribution obtained through experiments have been applied. The model accounts for the space charge effect of the charged particles and the turbulence dispersion on the particle trajectories. It was found that the space charge plays an important role for the final spray pattern shape, also increasing the transfer efficiency. The numerical results, such as velocity profiles, static and dynamic film thickness on the target were in good agreement with experiment.     

用于电介质中空间电荷分布测量的Tikhonov反卷积算法

研究了使用压力波法测量平板电介质试样的空间电荷分布的数值解法,使用基于Tikhonov正则化方法的反卷积算法得到了真实的空间电荷分布.在反卷积算法中使用了相关的技术处理,如小波包过滤高频噪音,Tikhonov正则化方法处理积分方程等.利用数值实验研究了噪声对反卷积算法的影响,结果表明,在无噪或者低噪环境下,反卷积算法能够非常好地计算出电介质中的空间电荷分布;在处理有噪数据时,反卷积的结果受到明显的影响,但仍然有较高的计算精度.正则化参数α对空间电荷分布的数值解起着明显的光滑作用,但是对于解的积分值却影响不大.对实际测量数据进行处理的结果表明,反卷积算法成功地计算出了固体电介质中的空间电荷分布和电场分布.