水平表面气流剪切作用下的水膜厚度

飞机结冰表面上的液态水受气流吹拂作用会发生向后溢流,从而影响结冰区域范围及防冰系统设计;为了获得水膜流动规律,对水平平板表面上气流剪切驱动的水膜流动进行了实验测量和建模分析。通过水膜流动风洞试验台产生高速气流驱动水膜的流动,使用色散共焦位移计测量同一位置的水膜在不同时刻的厚度变化,结果表明气-液界面由底层薄水膜和多种尺度的波动组成,具有变化速度快随机性强的特点。通过水膜厚度随气流速度及水膜雷诺数的变化规律,发现平均水膜厚度与两者均呈现出单调非线性的依赖关系。基于薄水膜流动理论和平均水膜厚度实验结果,提出了高速气流剪切作用下的气-液波动界面剪切因子计算式,适用于风速17.8~52.2m/s,水膜雷诺数26~128之间的平板水膜流动计算。     

我国可重复使用液体火箭发动机发展的思考

重复使用是降低航天发射成本的重要途径之一,是液体火箭发动机未来发展的重要方向。本文分析了可重复使用液体发动机的发展趋势,针对可重复使用运载器对发动机功能的需求,探讨了动力系统方案;对比了液氧煤油和液氧甲烷等推进剂组合和不同循环方式,认为几种发动机方案均可满足重复使用运载器的需求;研究了重复使用发动机的关键技术,提出应重点研究可重复使用液体火箭发动机高温组件热结构疲劳寿命评估及延寿技术、运动组件摩擦磨损技术、结构动载荷控制与评估技术、快速检测评估与维修维护技术、健康监控与故障诊断技术、二次或多次起动技术与大范围推力调节技术等。     

针栓式喷注单元膜束撞击雾化混合过程数值模拟

为了全面认识针栓式喷注器喷雾场结构，基于自适应网格加密技术和分三相计算的PLIC VOF（Piecewise Linear Interface Calculation Volume of Fluid）方法对针栓式喷注单元膜束撞击雾化混合过程进行了仿真分析，通过对两路推进剂分别进行界面追踪，获得了膜束撞击雾化混合过程的详细结构特征，与高速摄影试验结果定性定量对比均吻合较好，验证了数值方法的准确性。以此为基础对膜束撞击的喷雾场结构、撞击变形过程、流场涡结构、雾化破碎典型特征及破碎后的雾化混合分布特征进行了识别分析，结果表明：膜束撞击形成了液束未穿透液膜和液束穿透液膜2种不同的喷雾扇结构。膜束撞击形成的喷雾扇呈"Ω"形，膜束同时发生弯曲变形和横截面变形。另外，膜束撞击同时受到正压和剪切应力作用，导致了一系列复杂涡流现象，使得相互作用增强，雾化混合均增强，这也是膜束撞击喷注构型优于膜膜撞击的本质原因。最后，还发现膜束撞击喷雾场液滴分布呈现分区结构特征，分别是液束控制主导的上雾化区、液膜控制主导的下雾化区及夹在中间的混合区，实际中应兼顾雾化特性和混合特性，选取中等动量比膜束撞击，这可为针栓式喷注器的理论研究和工程设计提供重要参考。     

动叶顶部间隙结构对涡轮性能影响的数值分析

富氧燃气中工作的涡轮动叶顶部间隙较大,导致泄漏损失很大。通过对四种不同动叶顶部结构的涡轮级进行流场数值模拟,比较了其对涡轮性能、流场的影响。结果表明,动叶顶部围带与壳体迷宫结构的泄漏量最小,因而效率损失最小。     

7075铝合金在不同温度盐水环境中的腐蚀疲劳行为

基于飞机结构材料7075铝合金在沿海地区服役时海水飞溅及曝晒导致的高温腐蚀疲劳损伤问题,研究了7075铝合金在35,55,75℃下3.5%NaCl溶液环境中的腐蚀疲劳寿命,并使用扫描电子显微镜(SEM)观察断口形貌,探讨了温度对腐蚀疲劳裂纹萌生扩展的影响机理。结果表明:同一应力水平下,温度越高,腐蚀疲劳寿命越短,300MPa时35,55,75℃下的中值寿命分别为33 001,30 931,15 346次循环。腐蚀损伤和疲劳损伤存在竞争关系,应力水平较高时,腐蚀较轻,试样寿命主要受应力水平影响,疲劳源多从铝合金基体与包铝层结合处萌生;应力水平较低时,腐蚀较严重,疲劳寿命随温度升高明显下降,疲劳源多从腐蚀坑处萌生。断口形貌显示高温环境主要通过加速腐蚀坑的形成来影响疲劳源的萌生,深坑状腐蚀坑应力集中严重,对疲劳性能伤害大。     

A nonlinear background removal method for seismo-ionospheric anomaly analysis under a complex solar activity scenario: A case study of the M9.0 Tohoku earthquake

A precise determination of ionospheric total electron content (TEC) anomaly variations that are likely associated with large earthquakes as observed by global positioning system (GPS) requires the elimination of the ionospheric effect from irregular solar electromagnetic radiation. In particular, revealing the seismo-ionospheric anomalies when earthquakes occurred during periods of high solar activity is of utmost importance. To overcome this constraint, a multiresolution time series processing technique based on wavelet transform applicable to global ionosphere map (GIM) TEC data was used to remove the nonlinear effect from solar radiation for the earthquake that struck Tohoku, Japan, on 11 March, 2011. As a result, it was found that the extracted TEC have a good correlation with the measured solar extreme ultraviolet flux in 26–34 nm (EUV_26–34) and the 10.7 cm solar radio flux (F_10.7). After removing the influence of solar radiation origin in GIM TEC, the analysis results show that the TEC around the forthcoming epicenter and its conjugate were significantly enhanced in the afternoon period of 8 March 2011, 3 days before the earthquake. The spatial distributions of the TEC anomalous and extreme enhancements indicate that the earthquake preparation process had brought with a TEC anomaly area of size approximately 1650 and 5700 km in the latitudinal and longitudinal directions, respectively.     

Solar activity dependence of total electron content derived from GPS observations over Mbarara

Vertical total electron content (VTEC) observed at Mbarara (geographic co-ordinates: 0.60°S, 30.74°E; geomagnetic coordinates: 10.22°S, 102.36°E), Uganda, for the period 2001–2009 have been used to study the diurnal, seasonal and solar activity variations. The daily values of the 10.7 cm radio flux (F_10.7) and sunspot number (R) were used to represent Solar Extreme Ultraviolet Variability (EUV). VTEC is generally higher during high solar activity period for all the seasons and increases from 0600 h LT and reaches its maximum value within 1400 h–1500 h LT. All analysed linear and quadratic fits demonstrate positive VTEC-F_10.7 and positive VTEC-R correlation, with all fits at 0000 h and 1400 h LT being significant with a confidence level of 95% when both linear and quadratic models are used. All the fits at 0600 h LT are insignificant with a confidence level of 95%. Generally, over Mbarara, quadratic fit shows that VTEC saturates during all seasons for F_10.7 more than 200 units and R more than 150 units. The result of this study can be used to improve the International Reference Ionosphere (IRI) prediction of TEC around the equatorial region of the African sector.     

Response of the EIA ionosphere to the 7-8 May 2005 geomagnetic storm

In this paper, response of low latitude ionosphere to a moderate geomagnetic storm of 7–8 May 2005 (SSC: 1920 UT on 7 May with Sym-H minimum, ∼−112 nT around 1600 UT on 8 May) has been investigated using the GPS measurements from a near EIA crest region, Rajkot (Geog. 22.29°N, 70.74°E, Geomag.14°), India. We found a decrease in total electron content (TEC) in 12 h after the onset of the storm, an increase during and after 6 h of Sym-H deep minimum with a decrease below its usual-day level on the second day during the recovery phase of the storm. On 8 May, an increase of TEC is observed after sunset and during post-midnight hours (maximum up to 170%) with the formation of ionospheric plasma bubbles followed by a nearly simultaneous onset of scintillations at L-band frequencies following the time of rapid decrease in Sym-H index (−30 nT/h around 1300 UT).     

高速走丝电火花线切割表面条纹的成因研究

分析了高速走丝电火花线切割加工时可通过电极丝空间位置稳定性的改善及选用具有良好洗涤能力的工作介质进行条纹消除的机理.并研究指出在大能量切割时,选用复合工作液以喷射的方式进行冷却,可以大大提高极间的洗涤性能,达到消除表面烧伤纹的目的.     

Seasonal dependence of TEC and SLAB thickness

Several years of hourly daily GPS measurements of the vertical total electron content (TEC) and of the equivalent slab thickness made at different European locations are analysed by using the linear regression technique to demonstrate the response of these two ionospheric parameters to seasonal variations. It is found that both TEC and slab thickness are highly correlated with season. Analytical relationships are determined expressing the seasonal dependence of the vertical TEC and of the equivalent slab thickness as a function of the seasonal parameter cos χ at noon in each location.