Ion thruster accelerator grid erosion mechanism under extreme conditions of cylindrical erosion and chamfer erosion

In this paper, the abnormal experimental phenomenon on barrel erosion under extreme working conditions in the ultra-long life experiment(>10000 h) of ion thruster ion optics is studied by the Immersed-Finite-Element Particle-In-Cell Monte-Carlo-Collision(IFE-PIC-MCC) method and the grid erosion evaluation model. The transport process of beam ions and Charge Exchange(CEX) ions in the grid system, and the characteristics and mechanisms of the aperture barrel erosion under extreme erosion condit...     

北斗星基增强电离层模型精度评估与分析

针对如何有效地对北斗星基增强系统(SBAS)电离层在模型精度、模型时效性等方面进行综合评估,提出了一种修正的CODE格网模型,通过增加国内陆态网监测站观测数据,提升了CODE格网模型精度。以此模型为基准,利用2020年近一个月的数据分析了北斗区域格网电离层模型和北斗SBAS电离层模型的延迟误差、改正比例的变化以及在全球的覆盖范围,并从全球不同纬度带比较了北斗基本导航和星基增强电离层模型的精度。结果表明修正的CODE模型精度符合评估要求,且与我国电离层实际变化情况更吻合,北斗区域格网电离层模型和北斗SBAS电离层模型精度相当,优于0.3m,改正比例均优于80%,但北斗SBAS电离层模型覆盖范围明显更大。     

A compressing and saving method for structured grid data based on block construction

The increasing grid data in CFD simulation has brought some new difficulties and challenges, such as high storage cost, low transmission efficiency. In order to overcome these problems,a novel method for compressing and saving the structured grid are proposed. In the present method,the geometric coordinates of the six logical domains of one grid block is saved instead of all grid vertex coordinates to reduce the size of the structured grid file when the grid is compressed. And all grid vertex co...     

基于静气动弹性效应的飞机型架外形修正方法研究

民用客机主要针对巡航外形设计,这就需要通过静气动弹性修正得到型架外形,保证型架外形在设计巡航状态飞行时,气动性能能够恢复到巡航设计状态。本文基于混合网格的N-S方程和结构柔度矩阵方法的耦合求解,发展了大飞机静气动弹性计算方法。根据静气动弹性变形过程的可逆性,结合飞行器质量分布、发动机推力以及巡航飞行重量等设计参数,发展了考虑静气动弹性效应的飞机型架外形修正方法。利用所发展的修正方法,获得了某大型客机巡航飞行的型架修正外形,同时分析了其它飞行工况的弹性气动特性,并通过算例比较验证了本文发展方法的有效性。     

Enhancement on parallel unstructured overset grid method for complex aerospace engineering applications

In the present study, an efficient overset grid method by means of parallel implicit hole-cutting is proposed for the sake of simulating unsteady flows in aerospace engineering involving multiple bodies in relative movement. In view of the degraded computational efficiency and robustness for conventional overset grid assembly, several innovative techniques are developed within the overset grid assembly process, viz., a bookkeeping alternative digital tree method to speed up the donor-cell search...     

Radially loading rotary extrusion for manufacturing large-size conical cylinders with inner transverse high ribs

The Large-size Conical Cylinders with Inner Transverse High Ribs (LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion (RLRE) forming technology can achieve integral forming of LCCWITHR through the synergy of radial and rotary movements of dies. The flow law of the material during the forming process is the key to forming large-size inner ribs. At present, there is no unified understanding of the metal flow law of RLRE forming technology. An analytical expression was derived to predict the Radial Direction (RD) deformation loads. The FE simulation and process experiment were carried out to investigate the effects of the inclination angle, thickness factor and transition arc radius of the split top dies on the spacing of the metal diversion plane, the metal flow velocity of the rib area and the final radius of the inner rib. The influence of the split top dies loading distance and the bottom die rotation angle of each pass on the inner radius of the inner rib was verified. And the optimal combination of dies shape parameters and loading paths which can make the metal flow orderly was obtained: the inclination angle is 140°, the thickness factor is 3.64, the transition arc radius is 16 mm; the top dies loading distance is 15 mm, the bottom die rotation angle is 45°. The FE simulation results have been found to be in close agreement with physics experiment. The research results reveal the metal flow law of rib growth in the RLRE of LCCWITHR, which lays a theoretical foundation for subsequent thorough research and process optimization.     

Plasma transport simulation under different conditions and optimization analysis of dual-stage grid ion thruster

In order to study the extraction and acceleration mechanism of the dual-stage grid, a three-dimensional model based on the Particle-In-Cell/Monte Carlo Collision(PIC/MCC) method is performed. Dual-stage grid ion thruster is a new type of electrostatic ion thruster, which can break through the limitations of traditional gridded ion thrusters, and greatly improve the specific impulse. The high performance also makes the grid sensitive to operating parameters. In this paper,the influence of grid pa...     

一种涵道螺旋桨性能预测的CFD方法

为适应高性能涵道螺旋浆精细化设计需求,基于雷诺平均Navier—Stokes控制方程和非结构网格旋转／静止滑移面技术,开展了涵道与螺旋桨动／静部件干扰的非定常流及性能预测数值模拟方法研究。提出了．静止与旋转域的多块网格布局策略及转／静滑移面技术,研究了涵道壁而与螺旋桨桨梢间隙的网格布局形式,有效解决了螺旋桨旋转流及螺旋...     

肋参数对液氧甲烷发动机推力室强化换热的影响

为深入研究带肋推力室强化传热的机理，对带肋液氧/甲烷推力室的燃烧与再生冷却进行了流动与传热耦合分析，并针对不同肋高和肋数目进行了参数化分析。结果表明:引入等效平均热流密度的概念可以准确描述带肋推力室中的实际传热过程;平均热流密度总是随着肋数目的增加而减小，当肋高恒定时，由于总换热面积增大，等效平均热流密度会随着肋数目的增加而增大;而当总表面积恒定时，等效平均热流密度会随肋数目的增加而减小。此外，盲目地增大总换热面积并不一定能改善传热强化，甚至会在某些情况下恶化传热，因此在设计过程中也应该结合其他肋参数进行综合考虑。     

往复节流式正脉冲发生器性能分析CSCD

在石油开采与钻探领域,脉冲发生器作为旋转导向系统井下信号传输系统的重要组成部分,提高压力脉冲幅值有助于提升旋转导向系列产品的市场竞争力。为了揭示其工作原理及提高压力脉冲幅值,基于计算流体动力学,利用用户自定义函数(UDF)、动网格技术、非牛顿流体模型,借助Fluent平台对往复节流式正脉冲发生器进行了动态数值实验。利用离散形式的动量方程将主阀体与电磁阀的被动运动转变为主动运动,选择适用于k-ε湍流模型的赫-巴非牛顿流体本构方程描述泥浆,提高了计算的收敛性与运动的可控性。基于非牛顿流体的流固耦合方法,更真实地模拟了脉冲器在井下工作过程。结果表明限流环内径越小或入口排量越大,则压力脉冲幅值与信号发生频率越大。