高空来流条件下航空发动机双旋流燃烧室点火特性数值模拟

为深入了解真实航空发动机燃烧室极端条件下点火性能,在自有CFD平台上对不同高空来流条件下典型航空发动机双旋流燃烧室点火过程进行了数值模拟。为保证模拟精度,对模型包括全部气膜冷却小孔在内的所有精细结构均进行了完全仿真,并完整再现了燃烧室内从燃油雾化到点火燃烧全过程。结果表明3种高空来流条件下单次点火均失败。点火过程显示高温燃气越过旋流杯中心向上回流区扩张是点火的关键时空区域,在此时补充点火可推动火焰顺利传播到整个主燃区。对8km和6km两种状态分别增加点火次数到3次和5次后最终点火成功,结果表明前者着火极限油气比约为0.057,后者为0.038~0.042。     

航天运载器力学环境工程技术发展回顾及展望

近50年来,航天科技工作者对运载器发射飞行过程中的力学环境的认识逐步深入,带动了相关基础理论、预示方法、分析工具、试验技术和试验设备的不断发展。随着航天技术的快速发展,对运载器等的设计要求越来越高,火箭经受的力学环境也越来越恶劣,火箭力学环境预示与试验技术研究的迫切性日益突出。文章综合分析了力学环境预示与试验技术领域的研究发展状况,重点总结了北京强度环境研究所50年来为解决航天工程中的诸多力学环境问题所做的具体工作。最后,结合新时期航天项目的工程需求,提出了今后在航天运载器力学环境预示与试验技术研究领域的主要研究方向。     

深空极低温服役环境下材料力学/物理性能低成本快速评价方法研究进展

随着我国空间探测卫星、深空探测飞行器等国家战略装备的快速发展,宇航材料的服役环境越来越苛刻,常常面临极端低温的考验。然而低温下材料的力学/物理性能和常温相比有很大差异,极低温使役环境下材料力学/物理性能评价成为人们关注的重点问题。本文着重对基于力-热能量密度等效原理而发展的深空极低温服役环境下材料屈服强度、弹性模量、理想拉伸强度、硬度等力学性能的低成本快速评价方法研究进展进行了总结和回顾;同时,介绍了力-热能量密度等效原理在低温下半导体材料的带隙能、折射率、拉曼频移,金属材料磁晶各向异性常数等物理性能的低成本快速评价方面的推广应用情况。该评价方法为实现地面实时监测在轨航天器中关键材料的主要力学/物理性能提供了有效途径,为国家高端技术装备建设中关键材料的设计、可靠性评价和实时性能监测等提供重要的手段。     

Multi-objective design optimization of the transverse gaseous jet in supersonic flows

The mixing process between the injectant and the supersonic crossflow is one of the important issues for the design of the scramjet engine, and the efficiency mixing has a great impact on the improvement of the combustion efficiency. A hovering vortex is formed between the separation region and the barrel shock wave, and this may be induced by the large negative density gradient. The separation region provides a good mixing area for the injectant and the subsonic boundary layer. In the current study, the transverse injection flow field with a freestream Mach number of 3.5 has been optimized by the non-dominated sorting genetic algorithm (NSGA II) coupled with the Kriging surrogate model; and the variance analysis method and the extreme difference analysis method have been employed to evaluate the values of the objective functions. The obtained results show that the jet-to-crossflow pressure ratio is the most important design variable for the transverse injection flow field, and the injectant molecular weight and the slot width should be considered for the mixing process between the injectant and the supersonic crossflow. There exists an optimal penetration height for the mixing efficiency, and its value is about 14.3 mm in the range considered in the current study. The larger penetration height provides a larger total pressure loss, and there must be a tradeoff between these two objection functions. In addition, this study demonstrates that the multi-objective design optimization method with the data mining technique can be used efficiently to explore the relationship between the design variables and the objective functions.     

1200℃高温环境下板结构热模态试验研究与数值模拟

高超声速飞行器高马赫数飞行时,翼、舵及垂尾等板形姿态控制结构将会面临极为严酷的高温环境,为了获得难于实测的结构在高温与振动复合环境下的热模态参数,本文将瞬态气动热试验模拟系统与振动试验系统相结合,建立了高温热/振联合试验测试系统,实现了高达1200℃热环境下矩形板结构的模态频率等关键振动参数的试验测试。同时,对矩形板结构的热模态特性进行了数值计算,并将试验结果与计算结果进行对比验证。试验中通过自行研制的耐高温陶瓷导杆引伸装置将结构上的振动信号传递至高温热场之外,使用常温加速度传感器对振动信号进行参数识别;并运用时-频联合分析技术对试验数据进行分析处理。本文所获得的高温环境(200~1100℃)下矩形板结构的模态频率的试验结果与数值计算结果取得了比较好的一致性,验证了本试验方法的可信性及可用性。本研究结果为高超声速飞行器翼舵结构在高温环境下的振动特性分析以及安全可靠性设计提供了重要的试验手段和参考依据。     

单圈分子图的第一广义Zagreb指标的极值

第一广义Zagreb指标定义为0Rα（G）=∑i∈V（G）d（i）α,其中d（i）为i顶点的度,α为除0和1之外的所有实数。单圈分子图是指最大度不超过4且边数等于顶点数的简单连通图。本文通过一个引理,给出了单圈分子图的第一广义Zagreb指标达到极值的必要条件。     

球形轨道分子屏极高真空系统的抽气方程

地面真空系统中,气体处于封闭的真空容器内,达到平衡状态时,压力 P 与抽速 S 的关系是:P=OIS;轨道分子屏极高真空系统是开放的(或者说具有部分真空容器),相应的抽气方程应该是怎样的形式呢?文章提出了一个物理模型,推导出了球形轨道分子屏极高真空系统的抽气方程。     

Reliability of satellite-based precipitation products in capturing extreme precipitation indices over Iran

The goal of this study is to assess the performance of four widely-used satellite precipitation products in capturing extreme precipitation indices across Iran over the period 2001–2018; these products include GPM IMERG (Integrated Multi-Satellite Retrievals for Global Precipitation Measurement), TRMM 3B42 (Tropical Rainfall Measuring Mission), CHIRPS (Climate Hazards Center InfraRed Precipitation with Station data), and PERSIANN-CDR (Precipitation Estimation From Remotely Sensed Information Using Artificial Neural Networks-Climate Data Record). For this aim, a national gridded precipitation dataset was developed using a dense network of rain gauges as a reference dataset. The results suggest that the IMERG product outperforms the other three precipitation products in capturing extreme precipitation indices both temporally and spatially. TRMM 3B42 data show promising results in identifying many extreme indices, while the CHIRPS and PERSIANN-CDR products show less performance in accurately generating many of the extreme precipitation indices.     

A study of the plasmasphere density distribution using computed tomography methods from the EUV radiation data

In this paper, we introduce a new topic for imaging plasmasphere density with CT techniques. Both parallel-beam and fan-beam reconstruction formulas are derived with a special weighting function. Different from the traditional X-ray CT, the extreme ultraviolet (EUV) radiation may be totally absorbed by the Earth. Only the portion between the Earth and the detector enters the EUV sensor and be measured. The key step in our derivation is to remove the complete absorption effect with a specific weighting function. Computer-simulation studies are present to verify our formulas for the plasmasphere density.     

航空网络关键节点辨识的核极限学习机算法研究

通过技术手段准确识别航空网络的关键节点,对航空网络平时的正常运行以及战时的防御和修复,具有重要的理论意义和参考价值。提出一种基于核极限学习机的航空网络关键节点识别方法,首先,采用层次分析法对节点综合重要度进行评估;然后,选取三个简单指标,基于核极限学习机学习简单指标与综合重要度之间的映射关系,建立重要度评估模型;最后,以中美两国航空网络为例进行仿真。结果表明:仅需计算 40 个节点的复杂指标值,就可对关键节点取得较满意的辨识效果,降低了计算复杂度,提高了辨识效率,即采用本文方法辨识航空网络的关键节点是有效、可行的。