北斗星基增强系统双频多星座服务覆盖范围评估

双频多星座(DFMC)服务已成为星基增强系统(SBAS)未来能力提升的重要方向之一,相关国际标准也将在2023年11月正式发布。北斗星基增强系统(BDSBAS)是全球范围内唯一持续播发DFMC增强服务测试信号的星基增强系统。在详细介绍SBAS DFMC服务可用性和保护级计算方法的基础上,利用实测的BDSBAS B2a增强电文对BDSBAS DFMC增强服务的一类垂向引导进近(APV-Ⅰ)/垂向导航信标性能(LPV)和决断高度200英尺垂向导航信标性能(LPV-200)等级的服务覆盖率进行了初步评估。评估结果表明,当前BDSBAS DFMC增强服务能够实现对中国及周边广大区域的服务覆盖,且双系统(BeiDou navigation satellite system和global positioning system, BDS+GPS)增强服务的APV-Ⅰ和LPV-200等级99%可用性覆盖率比单系统(BDS)增强服务的覆盖率分别提升16%和32%。     

卫星双向法与卫星测距

卫星双向时间比对是目前远距离台站时间比对精度最高的时间同步技术,时间比对精度达几百皮秒,比GPS共视技术的时间比对精度几乎高一个数量级。中科院国家授时中心根据多台站卫星时间比对经验,提出利用卫星双向比对技术进行卫星测距(称转发器定轨)。实验证明:利用卫星双向技术(卫星需要转发器)进行卫星测距,可得到高精度卫星轨道(内符精度为几厘米)和卫星预报轨道。     

A boundary surrogate model for micro/nano grooved surface structure applied in turbulence flow control over airfoil

The application of grooved surface structure is an emerging and effective means in turbulence flow control. However, for a realistic configuration, the global flow field described directly by simple application of massive grids makes it unfeasible to simulate. In this paper, a boundary surrogate model reproducing the effect of microscopic near-wall region is proposed to improve computational efficiency. The surrogate model trained with Lattice Boltzmann Method(LBM) considering the rarefied effec...     

90°圆截面弯管内三维紊流场实验研究

用CTA热线风速仪和五孔探针, 对一曲率直径比R_c/D=0.87, 直径D=280mm的90°圆截面弯管内部三维紊流流场进行了详细测量和分析。给出了不同雷诺数下弯管内不同截面上时均速度场、紊流动能、总压及静压沿曲率半径方向的分布。      

S弯进气道旋流缩涡实验研究

本文提出的旋流缩涡法采用了一种结构简单的缩涡器, 是一个金属薄片弯成的框架。这个缩涡器框架被安置在进气道喉道前, 通过4个薄片固定在模型上。实验研究表明:该法可缩小由S弯进气道进口分离所造成的单涡旋流作用范围, 并提高出口截面平均总压系数。      

变截面梁式压电智能板振动控制的小波模式

基于 Daubechies小波理论的尺度函数变换 ,对于变截面悬臂板结构的弯曲建立了由压电片感应器的观测电量识别挠曲变形构形的显式关系式。此基础上 ,采用具有位移与速度信号负反馈控制律后 ,建立了抑制振动的压电动力控制程序。由于小波尺度函数逼近具有低带通性质 ,即具有自动滤除高频分量的能力 ,该控制程序将不会出现由观测溢出与控制溢出耦合而造成的控制失稳 (即在抑制低频 (阶 )扰动时系统激发出高频 (阶 )扰动的现象 )。数值仿真结果表明 :该控制方法所能控制的模态阶数与压电片数相同 ,而且其控制程序在抑制外界干扰方面是有效的。     

Si对TiAl合金高温抗氧化性能的影响

利用X射线衍射、扫描电镜、能谱仪等手段研究了TiAl-Si(原子数分数为0~20%)合金在1 173 K大气中24 h的恒温氧化.结果表明:Si元素可以有效地提高TiAl合金的高温抗氧化性能;随着Si含量的增加,氧化膜厚度依次减薄,TiO₂的含量逐渐减少,Al₂O3的含量逐渐增加,添加到10%左右时就有连续致密的Al₂O₃保护膜形成;Si在0~20%的添加过程中并没发现Si的氧化物生成.分析表明:Si对抗氧化性能的贡献可归结于Si与Ti有很好的亲和力,可以有效地降低Ti离子的活度、阻碍Ti离子的向外扩散, 相对来说增强了Al离子的活度,促进连续致密的Al₂O₃保护膜生成.      

冷气射流对壁式火焰稳定器流场特性及壁温分布影响数值研究

为了满足先进加力燃烧室对于值班火焰稳定器工作可靠性的要求,设计了一种带气冷结构的壁式火焰稳定器,并采用数值模拟的方法研究了不同冷却孔角度对壁式火焰稳定器流场特性及壁温分布的影响.研究结果表明:设计的气冷壁式火焰稳定器可以有效抑制冷侧转角处的流动分离,避免热侧高温燃气通过冷却孔倒流进冷侧;通过调节稳定器斜板和后板上的开孔...     

Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional (2D) numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.     

一个大挠度柱面弯曲板条的求解

本文应用付宝连的大挠度弯曲直梁的功的互等定理,求解一个柱面弯曲板条的挠曲面方程.