树脂基复合材料的分解防热效率

为了提高树脂基复合材料烧蚀中的热阻塞效应,同时避免因为加入过量树脂引起的复合材料脆性较大的问题,本文提出了引入可分解纤维改性的方法来解决这一矛盾.通过比较,筛选出了分解性质与酚醛树脂相似的可分解纤维,制备了改性纤维/酚醛复合材料.电弧风洞烧蚀试验结果显示,20 mm厚的改性纤维/酚醛在最高热面温度1 300℃、总加热时间600 s的条件下背面温升比相同条件下高硅氧/酚醛低约40℃,表现出很好的烧蚀防热性能,与材料设计的初衷相符.因此,引入可分解纤维的方法是一种有效改善复合材料性能的方法.     

高压涡轮工作叶片缘板阻尼结构设计分析

对某高压涡轮工作叶片缘板阻尼结构进行了阻尼效果计算及试验分析,试验结果表明:随着正压力的增加,阻尼比基本呈现为先增加后降低,然后在一定范围内波动的规律,阻尼比峰值出现在100~280N之间.计算得到一弯共振下的正压力为123~158N,与阻尼效果试验基本一致.分类比较了常用缘板阻尼结构形式的优缺点,改进完善后的阻尼片结构质量增加约30%,在激振力占气动力百分比分别为1%,3%及5%时,振动响应减幅分别为31%,21%及16%.     

基于CFD-DEM耦合数值模拟的全尺寸直升机沙盲形成机理

为了研究直升机发生沙盲时沙尘云在悬停流场中的状态和分布规律,采用基于雷诺平均Navier-Stokes方程和Menter 剪切应力输运（SST）k-ω湍流模型的数值模型,通过应用程序编程接口耦合基于Hertz-Mindlin （No Slip）碰撞接触模型的离散元模型,并基于"多球法"构建了更加真实的非球形沙尘颗粒,计算了沙尘颗粒在流场中的运动和分布状态。与可得到的试验结果进行对比,验证了数值方法的有效性,并进行了地效状态旋翼拉力系数、桨尖涡位置以及沙尘云形成的宏观轮廓图的计算。应用所建立的方法,对不同悬停高度的直升机地效流场进行了计算,给出了流场的涡量以及速度云图,着重对比了不同悬停高度下沙尘云中沙尘颗粒速度和分布情况,分析了地效流场对沙尘颗粒状态的影响及沙尘云的形成机理,并计算出了沙尘云宏观分布图。结果表明：流场中大部分沙尘颗粒只能在地表随流场扩散而并不能形成沙尘云;沙尘云中外层空间的沙尘浓度比内层高;位于桨盘平面下层区域的沙尘颗粒以径向运动为主,切向速度较小,而位于桨盘平面上层的沙尘颗粒速度方向各异,速度大小接近。     

Evaluation and analysis on positioning performance of BDS/QZSS satellite navigation systems in Asian-Pacific region

By using the observation data and products of precise obit and clock offset from Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) and GNSS Research Centre, Curtin University in this paper, the positioning performance of BDS/QZSS satellite navigation system has been analyzed and evaluated in aspects of the quantity of visible satellites, DOP value, multipath effect, signal-to-noise ratio, static PPP and kinematic PPP. The analysis results show that compared to BDS single system when the cutoff angle are 30°and 40°, the DOP value of BDS/QZSS combined system has decreased above 20%, and the quantity of visible satellites increased about 16–30% respectively, because of the improved spatial geometric configuration. The magnitude of satellite multipath effect of BDS system shows the trend of MEO?>?IGSO?>?GEO, which is consistent with that of QZSS satellite system, as the constellation structure of the two systems is similar. The variation tendencies of signal-to-noise ratio with respect to elevation angle of the two systems are almost the same at all frequencies, showing that at the same elevation angle the signal-to-noise ratio of MEO satellites is higher than that of IGSO satellites, as the higher obit is the lower transmitting power is obtained. For having a specially designed obit, the variation of signal-to-noise ratio of BDS system is more stable. However, the magnitude of signal-to-noise ratio of QZSS system appears the trend of frequency 3?>?frequency 2?>?frequency 1. The static PPP performance of the BDS/QZSS combination system has been improved more significantly than the BDS single system in E, N and U directions. When the cutoff angle are at 7°, 15° and 30°, the PPP accuracy is increased about 25–34% in U direction, 10–13% and 23–34% in E and N directions respectively. When the elevation angle is large (40°), compared to BDS single system at lower elevation angles (7° and 15°) the PPP accuracy of the BDS/QZSS combination system is improved above 30% in U direction. In kinematic PPP performance, compared to BDS single system, the accuracy, availability and reliability of the BDS/QZSS combination system has been improved too, especially at large elevation angles (30° and 40°), the kinematic PPP accuracy in E and U directions has been improved about 10–50%, and above 50% in U direction. It can be concluded that the combination with QZSS system can improve the positioning accuracy, reliability and stability of BDS system. In the future, with the improvement of the satellite construction of Japan’s QZSS system and the global networking of China’s BDS satellites, the QZSS satellites will contribute greatly to improve the positioning accuracy, reliability, availability and stability of GNSS systems in areas such as cities, mountains, densely-packed buildings and severely covered areas in Asian-Pacific region.     

弹性环式挤压油膜阻尼器减振实验研究

为研究弹性环式挤压油膜阻尼器(ERSFD)的减振效果,建立了可更换不同参数弹性环的转子实验系统,开展了ERSFD的减振效果验证实验,并对实验结果进行了对比和分析.研究结果表明:ERSFD对转子具有较明显的减振作用.供油前后转子系统的各阶临界转速相对变化不超过4.63％,说明ERSFD的油膜不会明显改变转子系统模态.ER...     

时序效应减小转子叶片表面非定常气动力的数值模拟

利用商用Numeca软件模拟了一个1.5级压气机中的时序效应现象,研究了导叶-静子周向相对位置变化时中间转子叶片表面非定常气动力及压力系数的变化。该1.5级压气机为南航低速压气机试验器(LSC)的简化结构,各排叶片数之比为1:1:1。为了孤立分析尾迹和势扰动的影响,还进行了导-转和转-静结构的计算。结果表明,通过调整导叶-静子的周向相对位置,可以使中间转子叶片表面非定常气动力的一阶响应幅值显著减小。     

基于体积力模型的大S弯进气道与风扇耦合计算研究

为理解超紧凑大S弯进气道与风扇的耦合效应,基于体积力模拟方法开展了一体化计算研究。研究的进气道长径比为2.5,使用Rotor 67进行耦合分析,体积力模型与冻结转子计算得到的总压比、总温比和等熵效率分别相差4.49%,0.26%和2.38%。流场分析表明,风扇对入口段流场影响较为明显,主要体现为畸变区的顺向偏转与微弱衰减;进气道出口畸变经过风扇叶片后得到改善,大低压区和反向旋流基本消失;而流体在叶片的前后缘旋流角与轴向速度的综合改变量越大,风扇对气流做功越多。总的来说,超紧凑大S弯进气道与风扇之间耦合比较明显,需要在设计时进行详细的考察。     

航天器迎风面不同位置原子氧掏蚀效应的数值模拟研究

Kapton作为基底的热控涂层被广泛应用于航天器的外表层设计中。近地轨道航天器的飞行方向与航天器表面法线之间的夹角(在本文中简称为ANI)对原子氧掏蚀效应有较大的影响。文章利用Monte Carlo方法研究了航天器迎风面(即0°≤ANI≤90°处)上ANI与掏蚀效应之间的关系。结果表明,束流和撞击能量不变时,ANI的增加会引起原子氧掏蚀空腔发生同向倾斜,空腔的深度不断减小,而宽度将急剧增加;当保护层厚度一定时,ANI的增加还会引起缺陷处入射的原子氧的反应率降低。     

航天器项目群管理模式探讨

阐述了我国现有航天器多项目管理的模式和特点,在分析我国航天器项目管理发展基础上,根据航天器研制任务急剧增长的情况提出了项目群管理的概念和项目群管理模式的思路,为寻找更好的适合航天器快速发展的项目管理方法提供参考。     

调频连续波无线电高度表的仿真研究

阐述了调频连续波无线电高度表工作原理和仿真模型，在分析中考虑了垂直速度形成的多普勒效应，文中给出几种仿真计算的结果，分析计算结果可得知高度表的工作稳定性以及多普勒效应引起的动态误差，仿真计算程序可以应用于优化伺服系统参量或制作高度表的数学仿真器等方面。