高能电子辐照下聚合物介质深层放电实验研究

为揭示聚合物介质材料在连续能谱高能电子辐射下的深层放电规律特征,利用~(90)Sr放射源对聚四氟乙烯(PTFE)材料进行了不同条件的辐照实验。对采集的大量放电数据进行统计分析发现,电子辐照累积时间、入射电子通量以及温度都会影响介质的放电风险以及放电脉冲特征。高能电子对样品持续数天的累积辐照会降低介质自发放电的阈值条件,辐照后期放电更加频繁,但放电强度会减弱。入射电子通量越低时,放电风险越小;通量越高时,放电频率越高,高强度放电事件的发生概率也越大。温度主要通过影响介质的电导率而影响其深层放电特性,温度下降时介质本征电导率降低,充电电位和放电风险增加;一旦发生放电,放电电流脉冲的平均幅度也更大。     

典型参数对盘缘封严性能综合影响机制

为了掌握典型参数对盘缘封严燃气入侵的综合影响机制,采用数值方法研究并揭示了燃气入侵形式与封严间隙涡系结构的内在联系,在此基础上设计了一种内环型盘缘封严结构。结果表明:增加转速和增加主流流量都会导致封严效率降低,但是二者的作用却是相互羁绊的;与传统孔口模型相比,内环型盘缘封严结构能够有效将回流区涡限制在封严间隙内,利用羁绊效应拓宽了高封严效率区域的工况范围,提高了盘缘封严性能。     

一种改进的虚拟永磁风力发电系统模拟平台

提出了一种包含风剪塔影效应的风力发电系统的改进型模拟方案。以背靠背三相变流器平台为基础,建立了考虑包含风剪塔影效应的虚拟永磁直驱风力发电系统的数学模型,进而搭建其控制系统；针对简化叶尖速比与转矩系数拟合的问题,提出了一种基于Kalman滤波的分段线性拟合的方法来简化拟合方程；利用MATLAB/Simulink仿真软件搭建虚拟风力发电系统模拟平台,对负载变化时的模拟平台输出以及有无风剪塔影效应时风力机的机械转矩变化进行仿真分析。仿真结果表明,该平台能够较好地模拟出风力机发电机组地运行特性。     

On the anthropogenic and natural injection of matter into Earth’s atmosphere

Every year, more and more objects are sent to space. The increasing number of countries with space programs, advancing commercialization, and ambitious satellite constellation projects raise concerns about space debris and the increase of mass flux into the atmosphere due to deorbiting of satellites and rocket bodies. A comparison of this anthropogenic influx to the natural influx due to meteoroids is presented giving detailed information about the mass, composition and ablation of the entering matter. Currently, anthropogenic material does make up about 2.8% compared to the annual injected mass of natural origin. For two different future scenarios considering planned and already partially installed large satellite constellations this fraction increases to nearly 13%, respectively 40%. For these cases, the anthropogenic injection of several metals prevails the injection by natural sources by far. Considering different ablation products, we find that the anthropogenic injection of aerosols into the atmosphere increases disproportionately. Today, they make up about 1% compared to the injected aerosol mass of natural origin, increasing to 30% and 94% for the two future scenarios, respectively. Considering the injection of atoms, the natural injection is dominant by far. For the two future scenarios, the anthropogenic injection is only at 5%, respectively 15% compared to the annual natural atom injection. The predicted strong increase in anthropogenic injection will make it significant in comparison to the natural injection which can have yet unknown effects on Earth’s atmosphere and the terrestrial habitat.     

Experimental study of curvature effects on jet impingement heat transfer on concave surfaces

Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects. The experiments were conducted by employing a piccolo tube with one sin-gle jet hole over a wide range of parameters: jet Reynolds number from 27000 to 130000, relative nozzle to surface distance from 3.3 to 30, and relative surface curvature from 0.005 to 0.030. Exper-imental results indicate that the surface curvature has opposite effects on heat transfer characteris-tics. On one hand, an increase of relative nozzle to surface distance (increasing jet diameter in fact) enhances the average heat transfer around the surface for the same curved surface. On the other hand, the average Nusselt number decreases as relative nozzle to surface distance increases for a fixed jet diameter. Finally, experimental data-based correlations of the average Nusselt number over the curved surface were obtained with consideration of surface curvature effect. This work con-tributes to a better understanding of the curvature effects on heat transfer of a round jet impinge-ment on concave surfaces, which is of high importance to the design of the aircraft anti-icing system.     

临近空间高超声速飞行器天文导航系统综述

临近空间是航天与航空业务领域的结合部，具有重要的战略价值。高超声速飞行器是临近空间力量部署的重要载体，已逐渐进入应用部署阶段。临近空间高超声速飞行器的飞行环境和任务条件对导航系统提出了新的更高要求。在总结临近空间高超声速飞行器的导航技术研究进展的基础上，对天文导航技术的应用环境和条件进行了系统的分析和探讨，提出了5个重点研究方向，包括：星图采集效能、光学误差模型、视场观测机理、姿态更新速率、小型化模块化工程化等。研究结果可为临近空间高超声速飞行器天文导航系统的设计提供参考。     

低温对涡轴发动机起动性能影响的试验与分析

为研究低温对涡轴发动机起动性能的影响,对国军标的适用与裁剪进行了讨论,开展了低温起动试验,试验以滑油箱内的滑油温度达到-34 ℃算起,冷浸4 h后进行起动,分析了低温起动过程的阻力矩、剩余扭矩、点火性能和温升效应对起动性能的影响。结果表明:-34 ℃条件下的初始阻力矩是25 ℃条件下的2.25倍,至点火转速附件阻力矩降低为1.53倍；温度越低,点火边界对应的索尔太平均直径(SMD)越小,燃烧室点火边界越窄；温升效应对低温起动性能的影响显著,考虑温升效应的起动时间延长约25%。热空气加温和起动滑油断油可以降低起动初始阻力矩,改善点火性能,从而提高了低温起动性能。研究结论对同类发动机开展低温起动试验、起动供油规律优化及相关研究提供了参考。      

地面效应下的不同翼型亚声速气动特性分析

采用数值方法研究了亚声速地面效应条件下不同翼型的气动特性,进一步以Ma=0.5来流工况为例,研究了翼型参数和飞行高度对气动特性的影响。计算结果表明在Ma为0.5、迎角为6°的地效情况下,翼型弯度减小,更容易在翼型前缘产生激波阻力;翼型下翼面后缘弯度增大使得后缘压力更高,升力系数和低头力矩相应增大;随着飞行高度的减小,地效作用加强,翼型下翼面压力增大,下翼面的升力增量大于上翼面吸力损失,机翼升力系数和升阻比增加越来越显著。     

航天系统雷电防护技术发展综述及展望

为满足航天系统的全天候发射任务需求，加强航天系统对于雷电环境的适应性，对航天系统雷电防护技术的发展情况进行了综述。首先分析雷电环境对于航天系统产生的破坏效应，追踪了世界航天史上典型的雷击案例，系统梳理了国内外航天系统雷电防护标准规范。针对运载火箭雷电效应数值仿真技术、雷电防护设计技术和试验验证技术，雷电气象监测预警技术，地面雷电防护技术和接地技术等关键技术的发展情况进行了追踪。在此基础上，从我国航天工程雷电防护的实际需求出发，对未来我国航天系统雷电防护技术重点研究方向进行了展望。     

水/金属燃料发动机水滴蒸发非傅里叶效应研究

水／金属燃料发动机单液滴蒸发拟选用表面模型假设,为了验证此假设的正确性,采用了修正的傅立叶定律,并分析了其物理意义及适用范围。通过试验验证及分析计算,从理论上证明,表面模型假设适用于水／金属燃料发动机水滴内部的输运过程。