空气预冷发动机及微小通道流动传热研究综述

首先针对发动机空气预冷系统的特点,将现有的预冷机制分为四种类型,包括燃料预冷、质量喷注预压缩冷却、燃料预冷和质量喷注预压缩冷却组合预冷以及其他流体预冷,并分别介绍了每种预冷机制的代表性发动机循环以及技术特点。调研发现,微小通道结构的预冷器具有很高的散热能力和紧凑度,优势显著。英国Skylon空天飞机的预冷却组合循环发动机（SABRE）其微通道结构预冷器具有极高换热能力。对SABRE的预冷器及相关研究进行详细分析,强调微小通道强化换热对提高发动机性能的重要作用。通过对微小通道中单相气态流动换热研究的调研发现,微尺度流动传热机理仍存在诸多分歧,理论发展不完善,需要深入开展微小通道强化传热研究,尤其对于高速高内外温差条件下微小尺度复杂结构空间内流动传热机理需要深入探索。     

Temporal and spatial variation of equatorial ionization anomaly by using multistation ionosonde data for the 19th solar cycle over the Indian region

The paper deals with the study of temporal and spatial variation of equatorial ionization anomaly (EIA) phenomenon along with its dependence on solar activity and season during the 19th solar cycle by using seven Indian ionosonde stations. Present study is an attempt to carry out the comprehensive study of EIA by using the limited number of ground based instruments. This has been achieved by performing the Gaussian fitting over the latitudinal distribution of F2-region critical frequency (foF2) data. Results reveal that the phenomenon of EIA has a strong dependence on solar activity and seasons. The EIA crest exhibits the feature of latitudinal shifting and expansion with increasing solar activity. It is found out that the effect of solar cycle and seasons on EIA is local time dependent. The observations were also compared with the IRI-2001 model predictions and results reveal that the model values are in general agreement with the observed values with some discrepancies, particularly during the high solar activity period and morning sector. The results have been discussed in the light of relative contribution from transequatorial interhemispheric neutral wind and strength of equatorial fountain process during different local time, season and solar activity levels. Furthermore, an attempt is made to parameterize the location and foF2 of the EIA crest by using the regression analysis. These results can be used to predict the latitudinal position and foF2 of the EIA crest for any given 12-month running average sunspot number (R12).     

全流量补燃循环发动机系统参数模型与设计(Ⅱ)参数设计

在全流量补燃循环发动机系统动力平衡模型的基础上,研究了氢发汗冷却流量、燃烧室压力和燃烧室混合比对发动机系统参数的影响规律.研究结果表明:在发动机推力和喷管扩张比保持恒定时,①随着氢发汗冷却流量的增加,燃料泵扬程大幅度增大,氧化剂泵扬程小幅度减小;②当燃烧室压力在20MPa之前,泵的扬程增加与燃烧室压力的增加近似成线性;...     

TC11焊接接头高周疲劳分形损伤模型

根据金属疲劳断口具有几何分形特征,将Chaboche高周疲劳损伤模型推广到分数维空间,建立了综合考虑断口细观特征的高周疲劳分形损伤演化模型.针对TC11钛合金电子束焊接接头,以载荷控制的疲劳试验为基础研究其高周疲劳性能;采用扫描电镜法(SEM)对断口微观特征进行定量分析,计算得到了各级载荷下疲劳断口的分形维数;通过对试...     

飞控系统极限环抑制对

舵机是电传飞控系统中非线性因素的重要组成部分,若参数选择不当,常会发生稳态不衰减的小幅值极限环振荡现象。应用非线性控制理论,将飞控系统稳定性要求转化为对舵机的幅频特性、相频特性和不灵敏区范围要求,从而通过舵机设计达到抑制极限环的目的。仿真结果表明,该方法简单、实用,具有较高的工程应用价值。     

我国载人登月重型运载火箭动力系统探讨

月球研究与利用是21世纪航天发展的重点之一。根据载人登月的需求,探讨了我国重型运载火箭及其动力系统的技术途径,提出研制大推力液氧/烃和液氧/液氢发动机的设想。重点论证了大推力下面级发动机的推进剂组合、动力循环方式及推力量级,认为该发动机推进剂应选择环保、廉价及高性能的液氧/烃组合,动力循环方式应采用先进的补燃循环或低成本的燃气发生器循环,推力应为4000kN左右。     

一种小型全流量补燃循环火箭发动机实验装置

介绍一种新的液体火箭发动机动力循环型式—全流量补燃循环的概念及其相对于其它动力循环的优点。为研究这一先进的循环系统,设计了一套小型全流量补燃循环氢/氧火箭发动机实验装置。结合该装置的系统方案,对其进行一维管路计算;通过对2个预燃室进行热力计算,确定了其燃烧温度和预燃气体的热物理性质;在燃烧室压强和混合比大范围变化的情况下,对氢氧推进剂的比冲特性进行探讨,以此确定燃烧室压强为4.0MPa,推进剂余氧系数为0.75。最后估算出该实验装置所能产生的推力为4018.77N。      

武器装备费用确定方法及效费比分析探讨

分析了武器装备的全寿命周期费用的构成及特点,提出用装各经济寿命分析的方法计算出装备的全寿命费用;分析了效能费用的辩证关系,对效费比计算进行了初步的探讨。     

利用相似周方法预测第24活动周开始时间

利用相似周方法对第24活动周的开始时间与第23活动周下降相后期的太阳黑子数进行了预报.根据第23周已经出现的特征参量和下降相的形态特征,选取9,10,11,15,17和20等六个太阳活动周作为第23周下降相的相似周,对第24周开始时间进行预报.预报结果显示,第24活动周的开始时间为2007年5±1月,黑子数平滑月均极小值为7.1±2.6,第23太阳活动周长度为11.1年.与其他研究者的预报结果相比较,本文给出的结果与文献[11]和[12]及MSFC的结果比较一致.通过对相似周方法在下降相预测太阳活动周结束时间的研究讨论,及对第23周上升阶段的太阳黑子数和F10.7平滑月均值预报结果的评估,可以看出,相似周预报方法在太阳活动周长期预报中是很有应用价值的.      

Comparison of convergence time and positioning accuracy among BDS,GPS and BDS/GPS precise point positioning with ambiguity resolution

Precise point positioning (PPP) usually takes about 30?min to obtain centimetre-level accuracy, which greatly limits its application. To address the drawbacks of convergence speed and positioning accuracy, we develop a PPP model with integrated GPS and BDS observations. Based on the method, stations with global coverage are selected to estimate the fractional cycle bias (FCB) of GPS and BDS. The short-term and long-term time series of wide-lane (WL) FCB, and the single day change of narrow-lane (NL) FCB are analysed. It is found that the range of GPS and BDS non-GEO (IGSO and MEO) WL FCB is stable at up to a 30-day-time frame. At times frame of up to 60?days, the stability is reduced a lot. Whether for short-term or long-term, the changes in the BDS GEO WL FCB are large. Moreover, BDS FCB sometimes undergoes a sudden jump. Besides, 17 and 10 stations were used respectively to investigate the convergence speed and positioning errors with six strategies: BDS ambiguity-float PPP (Bfloat), GPS ambiguity-float PPP (Gfloat), BDS/GPS ambiguity-float PPP (BGfloat), BDS ambiguity-fixed PPP (Bfix), GPS ambiguity-fixed (Gfix), and BDS/GPS ambiguity-fixed (BGfix). The average convergence speed of the ambiguity-fixed solution is greatly improved compared with the ambiguity-float solution. In terms of the average convergence time, the Bfloat is the longest and the BGfix is the shortest among these six strategies. Whether for ambiguity-float PPP or ambiguity-fixed PPP, the convergence reduction time in three directions for the combined system is the largest compared with the single BDS. The average RMS value of the Bfix in three directions (easting (E), northing (N), and up (U)) are 2.0?cm, 1.5?cm, and 5.9?cm respectively, while those of the Gfix are 0.8?cm, 0.5?cm, and 1.7?cm. Compared with single system, the BDS/GPS combined ambiguity-fixed system (BGfix) has the fastest convergence speed and the highest accuracy, with average RMS as 0.7?cm, 0.5?cm, and 1.9?cm for the E, N, U components, respectively.