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在低速来流条件下,针对前缘位置嵌有合成射流/合成双射流激励器的机翼的水滴撞击特性开展了数值模拟研究,基于Fluent软件,采用Euler气液两相模型和欧拉壁面液膜(Eulerian wall film,EWF)模型,得到的计算结果表明:在合成射流或合成双射流的主动控制下,阻挡了机翼前缘等积冰重点防护区域内的水滴撞击,从而大幅降低了该区域的结冰强度.其机理是:在高频合成射流的作用下,机翼前缘上游附近形成了一对稳定的闭合回流区,形成了水滴的"真空区域".由于回流区内部水滴速度和质量分数较低,改变了机翼前缘水滴运动轨迹和水滴收集率分布,能够减少机翼前缘结冰程度并改变冰形,起到了虚拟气动外形的作用. 相似文献
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应用N-S方程求解空气外流场和防冰腔内流场,用Euler法获得过冷水滴撞击特性,将内外流场进行耦合传热稳定后,开始结冰,来实现机翼热气防冰及冰脊形成的数值模拟.计算结果表明,热气防冰开启时,加热区蒙皮最低温度为286 K保证加热区没有结冰,但在加热区后的上下表面由于蒙皮温度降低至273.15 K以下,防冰区的溢流水到此处形成冰脊,这个计算结果表明了热气防冰数值模拟的可行性与合理性.但在将前缘积冰除去的情况下,防冰区外形成冰脊对气动特性影响很大,对带冰脊的机翼绕流流场进行数值模拟,对计算结果进行分析,得出环境温度越低、形成冰脊的位置越靠近防冰区,冰脊的高度越高;结冰时间越长,冰脊后的非定常特性越明显,流动细节的捕捉越困难,对气动特性的影响越大. 相似文献
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利用三维分子动力学模拟方法,研究了纳米尺度水滴撞击冷壁面的结冰过程.数值模拟中,统计系统采用微正则系综,势能函数选用TIP4P/ice模型,温度校正使用速度定标法,牛顿运动方程的求解采用文莱特算法,水滴内部结冰过程则通过统计垂直方向水分子温度分布来判定.研究发现,当冷壁面温度降低时,水滴完全结冰的时间减小,但水滴降至壁面温度的时间却增大;同时随着壁面亲水性降低,水滴内部热传递速度减慢(尤其是冷壁面与水滴底端分子层间),水滴内部温度趋于均匀,但水滴完全结冰时间延长. 相似文献
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基于行波管中慢电磁行波的周期传输特性和能流坡印廷定理,考虑高频结构的衰减、切断、螺距的渐变与跳变对互作用的影响,建立了螺旋线行波管三维场论非线性自洽工作方程组.通过傅里叶展式将时域中的电流变换为与频率相关的交流电流分量,采用等离子体粒子模拟的方法,求解离散化的亥姆霍兹方程获得空间电荷场的三维数值解.计算三维电子轨迹,得到精确的互作用后的电子能谱结构,为多级降压收集极的设计提供关键参数.计算结果与电子所Ku波段的测试值比较具有较好的一致性,并分析了互作用后的电子能谱结构,与多级降压收集极的实验基本符合.
关键词:
行波管
非线性注波互作用
空间电荷场
等离子体粒子模拟 相似文献
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该文结合了Ott提出的修正连续性方程和Adami改进的动量方程, 对空气中的液滴碰撞问题进行了二维数值模拟. 为有效提高计算精度, 推导了适用于大密度差多相流的人工黏性和人工应力方程. 通过表面张力作用下方形液滴自然变化和空气中两液滴互溶的算例, 验证了算法的有效性; 对不同韦伯数 (8.8, 19.8)、不同碰撞参数 (0, 0.5)下的液滴碰撞过程进行了数值模拟, 并与VOF方法对比,取得了较为一致的结果; 进一步计算多个韦伯数、多个碰撞参数下的液滴碰撞, 得到了空气中二维液滴碰撞结果分布图,与实验结果相符合. 结果表明, 该算法对于求解涉及大密度差多相流的液滴碰撞破碎问题十分有效,而且该方法容易拓展到三维, 从而为进一步模拟火箭发动机的二次雾化过程奠定了基础.
关键词:
光滑粒子流体动力学
大密度差
多相流
液滴碰撞 相似文献
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Current and space-charge density distribution calculation is of great significance for numerical analysis and design of high-current electron guns and beams. When the electrons’ thermal initial velocities are taken into account, though there have been some numerical methods published, the calculation is very complicated. By introducing equivalent meridional potential and projection trajectory theory, the curvilinear axis trajectory equation for electrons neighboring to a central curved trajectory in rotationally symmetric electro-magnetic fields is derived in first- and second-order approximations. The evolution equation of the current density distribution of toroidal electron sub-beams is derived and it can be used to calculate the current and charge density distribution in electron beams and guns in iteration calculation. A compact numerical algorithm for calculating round high-current electron guns and beams was developed and related program was written as well. As examples, the evolution of the current density distribution of a Pierce gun and a periodic magnetic focusing high-current electron beam is simulated. This proves that this method is effective and practical. 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2015,(9)
This paper proposes an automatic structure overset grid method, which utilizes the hole-surface optimization with one-step searching, wall-surface grid oversetting, and dynamic overset grid approaches to achieve the high adaptability of overset grids for complex multi-body aircrafts. Specifically, based on the automatic structure overset grids, the method first solves the coupling of Navier-Stokes(N-S) unsteady flow equation and 6DOF motion equation, and establishes the multi-body collision model. Then, the numerical simulation of unsteady flow for complex aircrafts' multi-body separation, the simulation of multi-body separating trajectory and the separation safety analysis are accomplished. Thus, the method can properly handle practical engineering problems including the wing/drop tank separation, aircraft/mount separation, and cluster bomb projection. Experiments show that our numerical results match well with experimental results, which demonstrates the effectiveness of our methods in solving the multi-body separation problem for aircrafts with complex shapes. 相似文献
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文章讨论了在库仑有心力作用下点电荷二维运动轨迹方程的不同解法:比耐方程法、Runge-Lenz矢量法以及速度积分法.比耐方程法是利用比耐公式求解微分方程,得出点电荷的运动轨迹;Runge-Lenz矢量法和速度积分法都是从点电荷的动力学方程出发,利用矢量积分得出一个常矢量,并应用该矢量分析得出点电荷的轨迹方程.3种方法得到的轨迹方程是一致的.计算表明,库仑有心力作用下的点电荷的二维运动轨迹为圆锥曲线,并分析了不同初始条件下圆锥曲线的类型. 相似文献
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一种模拟大密度比多相流的混合算法 总被引:1,自引:0,他引:1
在扩散界面法(diffuse interface method,DIM)的基础上提出一种能够处理大密度比(large density ratio)的多相流混合算法.流场信息通过格子波尔兹曼方法(lattice Boltzmann method,LBM)获得;相界面通过直接求解Cahn-Hilliard(C-H)方程确定.为保证在大密度比情况下求解界面方程的稳定性,采用二阶迎风格式来离散方程的对流项.通过对Rayleigh-Taylor(R-T)不稳定、液体中的气泡上升及液滴撞击干燥壁面的数值模拟,验证了方法的可行性. 相似文献
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《Current Applied Physics》2018,18(11):1368-1374
In this paper, forced vibration was used to regulate the droplet migration, fully recording the transient migration of droplets on a micro-textured substrate under the resonance frequency by a high-speed camera. The influence of resonance frequency and dynamic migration characteristics of droplets on the solid micro-texture surface under lateral vibration were researched. The experiment demonstrates that the driving force is caused by the difference between the left and right contact angles made the droplet oscillate and migrate, and as time t increases, the left and right contact points are periodically shifted and the amplitude of migration increases. Therefore, based on the droplet migration behavior and its force balance mechanism, a spring vibration model of migration behavior of the vibrating droplet micro unit was set up to predict the complete trajectory of its migration on a solid surface. The calculation results show that the theoretical displacement is less than the experimental displacement, and the longer the time, the larger the difference. Affected by the vibration, part of the droplet permeates through the micro-texture, resulting in the droplet losing height and the contact angle becoming smaller as well. While the other part of droplet overcomes the internal surface tension to migrate. 相似文献
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为了研究超短激光脉冲和液滴相互作用过程中电子密度和光场的变化,基于非线性麦克斯韦方程组和电离速率方程,构建了激光等离子体非线性瞬态时域耦合模型,对飞秒激光脉冲击穿微米量级水滴时的电子密度和光场的时空分布进行了计算.结果显示水滴的击穿阈值最小可达2 TW/cm~2,为同等条件下无边界水介质击穿阈值的1/4.随着脉冲能量增强,水滴内自由电子密度峰值区域逆着激光入射方向移动,且入射光越强,水滴对光传播的屏蔽越明显.光束在水滴出射端外部汇聚,汇聚点的光功率密度可达入射光的5倍,且时域波形出现压缩和变形.另外,水滴对激光能量的吸收系数随光强增大而增大,并最终趋于饱和. 相似文献
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L.H. Liu L. Zhang H.P. Tan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,97(3):446-456
In graded index medium, the ray goes along a curved path determined by Fermat principle, and the curved ray-tracing is very difficult and complex. To avoid the complicated and time-consuming computation of curved ray trajectory, the methods not based on ray-tracing technique need to be developed for the solution of radiative transfer in graded index medium. For this purpose, in this paper the streaming operator along a curved ray trajectory in original radiative transfer equation for graded index medium is transformed and expressed in spatial and angular ordinates and the radiative transfer equation for graded index medium in cylindrical and spherical coordinate systems are derived. The conservative and the non-conservative forms of radiative transfer equation for three-dimensional graded index medium are given, which can be used as base equations to develop the numerical simulation methods, such as finite volume method, discrete ordinates method, and finite element method, for radiative transfer in graded index medium in cylindrical and spherical coordinate systems. 相似文献