一种基于多模型算法的纯弹道式弹道落点预报方法

本文以落点预报技术在弹道目标预警中的应用为背景,主要解决在未知弹道系数情况下如     

Experimental investigation of flow and distortion mitigation by mechanical vortex generators in a coupled serpentine inlet-turbofan engine system

The performance of compact, aggressive ducts in advanced propulsion systems is limited by the internal flow separation coupled with the formation of secondary counter-rotating vortices that give rise to intensive flow distortions at the duct exit. An experimental investigation was conducted to study the flow field and passive suppression of flow separation and Aerodynamic Interface Plane (AIP) distortion in a serpentine air inlet duct. Tests were performed by a turbofan engine at several Engine Operating Points (EOPs) from 56% (idle) to 100% (max). A large total pressure deficit region arose at the upper part of the AIP, which was associated with the upper surface flow separation. Using the new mechanical S-type vortex generators in two longitudinal positions (VG1 and VG2), separation and loss were diminished at the upper part of the duct and AIP. The VG2 arrangement attained the maximum reductions in distortion coefficients which were 73.72%, 60.7% and 37.8% in DC(90°), DC(60°) and ΔP_C/P metrics, respectively. In the next step of the study, some unsteady aspects of the flow field were analyzed inside the duct. The separation onset and reattachment points were determined by the standard deviation of static pressure on the upper surface. The AIP spectral distribution showed that the boundary of low pressure and high pressure recovery regions was dominated by the maximum fluctuations. Furthermore, the PSD diagram of several probes at AIP revealed the vortex shedding frequency and its higher harmonics at separation region. The energy content of distinct unsteady spectral features in the bare configuration was significantly reduced using VGs, which showed the improvement of flow at the duct exit.     

Numerical Simulation of Unsteady Flow Around Forward Flight Helicopter with Coaxial Rotors

Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.     

不同叶片尾缘结构对流换热特性实验

为了研究不同叶片尾缘结构对对流换热系数的影响规律,设计了三种尾缘结构,并搭建了实验台,采用红外热像仪对叶片尾缘的壁温进行测量。研究结果表明,（1）三种尾缘结构的对流换热系数沿壁面的分布有很大差异,针对实验件I,对流换热系数存在一最大值,且最大值出现的位置随着吹风比的增加而逐渐远离气膜出口;（2）实验件II和III的对流换热系数沿壁面均呈现逐渐降低的趋势,但降低的规律二者又不相同;（3）在相同壁面位置,实验件III的对流换热系数最高,而实验件I的对流换热系数最低,因此可以认为,实验件III所示的尾缘结构更有利于对叶片尾缘更好的冷却。     

Seasonal variability of GPS-VTEC and model during low solar activity period (2006–2007) near the equatorial ionization anomaly crest location in Chinese zone

Variability of vertical TEC recorded at Fuzhou (26.1°N, 119.3°E, geomagnetic latitude 14.4°N), Xiamen (24.5°N, 118.1°E, geomagnetic latitude 13.2°N), Nanning (22.8°N, 108.3°E, geomagnetic latitude 11.4°N), China, during the low solar activity in 2006–2007 have been analyzed and discussed. Remarkable seasonal anomaly was found over three stations with the highest value during spring and the lowest value during summer. The relative standard deviation of VTEC is over 20% all the time, with steady and smooth variation during daytime while it has a large fluctuation during nighttime. The biggest correlation coefficient was found in the VTEC-sunspot pair with a value of over 0.5. It seems that solar activity has a better correlation ship than geomagnetic activity with the variation of VTEC and better correlations are found with more long-term data when comparing our previous study. The results of comparing observation with model prediction in three sites reveal again that the SPIM model overestimates the measured VTEC in the low latitude area.     

Satellite derived aerosol optical depth climatology over Bangalore,India

Climatological aerosol optical depths (AOD) over Bangalore, India have been examined to bring out the temporal heterogeneity in columnar aerosol characteristics. AOD values at 550 nm derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard NASA’s Terra and Aqua satellites, for the period of 2002–2011 have been analyzed (independently) for the purpose. Frequency distributions of the AOD values are examined to infer the monthly mean values. Monthly and seasonal variations of AOD are investigated in the light of regional synoptic meteorology. Climatological monthly and seasonal mean Terra and Aqua AOD values exhibited similar temporal variation patterns. Monthly mean AOD values increased from January, peaks during May and thereafter (except for a secondary peak during July) fall off to reach a minimum during December. Monsoon season recorded the highest climatological seasonal mean AOD, while winter season recorded the lowest. AOD values show an overall increasing trend on a yearly basis, which was found mainly due to sustained increase in the seasonal averaged AOD during summer. The results obtained in the present study are compared with that of the earlier studies over the same location and also with AOD over various other Indian locations. Finally, the radiative and climatic impacts are discussed.     

新时效制度处理的2024铝合金塑性性能分析

对由导电率和硬度实验初步确定的２０２４铝合金新时效制度进行了拉伸试验研究，并对拉伸塑性性能试验数据进行了数理统计分析。通过实验研究和分析，证明２０２４铝合金采用新的时效制度，在塑性性能方面满足适航要求。     

On prediction of re-entry time of an upper stage from GTO

The evolution of objects in geostationary transfer orbit (GTO) is determined by a complex interplay of atmospheric drag and luni-solar gravity. These orbits are highly eccentric (eccentricity >0.7) and have large variations in velocity and perturbations during a revolution. The periodic changes in the perigee altitudes of these orbits are mainly due to the gravitational perturbations of the Sun and the Moon. The re-entry time of the objects in such orbits is sensitive to the initial conditions. The aim of this paper is to study the re-entry time of the cryogenic stage of the Indian geo-synchronous launch vehicle, GSLV-F04/CS, which has been decaying since 2 September 2007 from initial orbit with eccentricity equal to 0.706. Two parameters, initial eccentricity and ballistic coefficient, are chosen for optimal estimation. It is known that the errors are more in eccentricity for the observations based on two line elements (TLEs). These two parameters are computed with response surface method using a genetic algorithm for the selected eight different zones, based on rough linear variation of the mean apogee altitude during 200 days orbit evolution. The study shows that the GSLV-F04/CS will re-enter between 5 December 2010 and 7 January 2011. The methodology is also applied to study the re-entry of six decayed objects (cryogenic stages of GSLV and Molniya satellites). Good agreement is noticed between the actual and the predicted re-entry times. The absolute percentage error in re-entry prediction time for all the six objects is found to be less than 7%. The present methodology is being adopted at Vikram Sarabhai Space Centre (VSSC) to predict the re-entry time of GSLV-F04/CS.     

Drag reduction research in supersonic flow with opposing jet

A CFD study on drag reduction in supersonic flow with opposing jet has been conducted. Flowfield parameters, reattachment point position and surface pressure distributions are obtained and validated with experiments. From the analysis on the physical mechanism of drag reduction, it shows the phenomenon that, when the opposing jet blows, the high pressure region is located between the bow shock wave and the Mach disk, which makes the nose region much lower pressure. As the pressure ratio increases, the high pressure region is gradually pushed away from the surface. Larger the total pressure ratio is, the lower of the drag coefficient is. To study the effect of the intensity of opposing jet more reasonably, a new parameter R_PA has been introduced by combining the flux and the total pressure ratio. The study shows that the same shock wave position and drag coefficient can be obtained with the same R_PA with different fluxes and the total pressures, which means the new parameter could stand for the intensity of opposing jet and could be used to analyze the influence of opposing jet on flow field and aerodynamic force.     

汽车制动系统关键技术研究

本文对盘式汽车制动时的受力进行了分析，建立了汽车制动的受力模型、对汽车的制动力分配情况进行了分析，给出了汽车的制动器制动效能因数和制动力距的计算方法；然后对汽车制动系统的评价指标进行了总结，最后利用软件编写程序得到汽车的同步附着系数，这些为汽车制动的研究奠定了基础。