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991.
992.
为探索涡-声效应对固体火箭发动机中压力振荡特性的影响,基于VKI (Von Karman Institute for Fluid Dynamics)发动机,通过改变挡板位置与燃气温度,对旋涡脱落引起的压力振荡进行了大涡模拟数值研究.耦合分析表明:挡板位于速度波腹附近,压力振荡最为严重;旋涡能量在输运过程中易于被湍流耗散,靠近喷管的二阶速度波腹处旋涡脱落压力振幅明显高于其它位置.解耦分析表明:温度对旋涡脱落频率影响不大,当旋涡脱落频率与声振频率分离后,压力振幅显著下降. 相似文献
993.
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995.
GPS伪卫星组合定位方法及在变形监测中的应用 总被引:1,自引:0,他引:1
针对GPS在城市高楼密集区、深山峡谷等区域所跟踪的可见星数目少且分布不佳导致定位精度下降,以及GPS系统本身在垂直方向定位精度较差的问题,提出GPS伪卫星组合定位新方法,利用伪卫星增强GPS技术提高定位精度。建立了GPS和伪卫星组合定位的观测模型,分析了伪卫星多路径效应的特点,给出了减弱伪卫星多路径误差的有效方法。对某大坝坝区的实测数据进行处理的结果表明,文中所提出的方法能有效地减弱伪卫星多路径效应产生的误差,GPS和伪卫星组合定位方法提高了系统的定位精度,特别是垂直方向的精度。 相似文献
996.
Shenggao Yang Libin Weng Yaguang Zhu Xu Yang Sihui Hu Peikang Xu Huan Zhang Weidong Pan Jie Shang Xing Su 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):46-55
We used the TEC (Total electron content) data of 5 min resolution obtained from the Madrigal database during solar-maximum winter (Nov. 6, 2000–Feb. 4, 2001) to study statistically the polar ionospheric plasma distribution response to different intensity and orientation of IMF By/Bz components. The sunlit high-density plasma extension from dayside to nightside is favored in negative IMF By and Bz conditions. With the magnitude of the negative Bz increasing, the time range corresponding to the distinct high-density extension feature expands, and the plasma density along the extension path enhances, which can be attributed to the interaction between dayside solar-produced ionization whose poleward limit is decided by terminator and convection extent mainly modulated by IMF Bz component. As for IMF By component influence on the sunlit plasma extension, the combination effect of convection and corotation electric fields is necessary to be considered. 相似文献
997.
《中国航空学报》2020,33(5):1433-1443
Corner stall predictions are important and difficult in axial compressors. However, all of the prediction models have proved to be ineffective for advanced compressor blades, which tend to use the combined sweep and dihedral. As for the prediction parameter DL, although it effectively modeled the effects of the adverse pressure gradient and secondary flow, it failed to predict the corner stall of curved blades because the model failed to consider the intersection of the boundary layer at the corner region. In this paper, the shape factor gradient Ψ of the boundary layer at the corner region was investigated by numerically studying specially shaped expansion pipes under different adverse pressure gradients. The improved prediction parameter DJ was presented based on the model of Ψ and the circumferential pressure gradient ξ. A comparison of the critical range of the prediction parameters DL and DJ was investigated using the NACA65 cascade database, which was established by a numerical method. Then, the stall criterion was validated according to the experimental results of various test facilities with different blade geometries and experimental conditions. The results show that the improved prediction parameter is able to predict the corner separation/stall flows and is in good agreement with the experimental results for axial compressors with three-dimensional designed blades. 相似文献
998.
《中国航空学报》2020,33(5):1476-1485
This paper presents an experimental study into dynamics of chamber pressure and heat release rate during self-excited spinning and standing azimuthal mode in NTO/MMH (nitrogen tetroxide/monomethylhydrazine) impinging combustion chambers. Nine cases including two combustion chamber configurations were conducted. The operating conditions of all unstable cases were located in the instability region according to Hewitt empirical correlation. The results show that chamber pressure oscillations keep pace with the corresponding OH* chemiluminescence intensity over the whole combustion region in the spinning and standing modes. It is indicated that the Rayleigh index is positive over the whole combustion area in all the unstable cases. A significant supersonic flame front structure of the first-order spinning mode was found in a cylindrical chamber, which means that a detonation wave could exist in the cylindrical chamber without a center body. The pressure and heat release rate oscillations at the pressure node are nonnegligible although their amplitudes are lower than those at the pressure antinode in the first-order standing mode with an annular chamber. Besides, the dominant frequency of pressure and heat release rate oscillations at the pressure node is twice as high as that at the pressure antinode. 相似文献
999.
《中国航空学报》2020,33(7):1929-1941
Aero-optical effects for starlight transmission in the high-speed flow field will reduce the accuracy of the star sensor on an aircraft. Numerical simulations for aero-optical effects usually require plenty of calculations, which cause difficulties when designing a celestial navigation system for a high-speed aircraft. In this study, an Aero-Optical Simulator For Starlight Transmission (AOSST) in the boundary layer is developed. It effectively reduces the computational burden compared to that of the widely used CFD simulation, and it achieves satisfactory accuracy. In this simulator, gas ellipsoids satisfying certain design rules are used to simulate coherent density structures in boundary layers. Design rules for the gas ellipsoids are found from published experimental and high-fidelity CFD simulation results. The generated wavefront distortion by AOSST is anchored with the scale law for aero-optical distortion in the boundary layer by determining some control parameters, which enables the simulator to output reliable results over a wide range of flight states. Four numerical examples are provided to verify the performance of AOSST. The results demonstrate that AOSST is able to simulate the directional dependence of aero-optical distortions in boundary layers, the variation trend of distorted wavefront shapes with Reynolds number, and the grayscale distribution on the disturbed star map. 相似文献
1000.
Wei Li Guangxing Wang Jinzhong Mi Shaocheng Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(5):1670-1680
The global navigation satellite system (GNSS) is presently a powerful tool for sensing the Earth's ionosphere. For this purpose, the ionospheric measurements (IMs), which are by definition slant total electron content biased by satellite and receiver differential code biases (DCBs), need to be first extracted from GNSS data and then used as inputs for further ionospheric representations such as tomography. By using the customary phase-to-code leveling procedure, this research comparatively evaluates the calibration errors on experimental IMs obtained from three GNSS, namely the US Global Positioning System (GPS), the Chinese BeiDou Navigation Satellite System (BDS), and the European Galileo. On the basis of ten days of dual-frequency, triple-GNSS observations collected from eight co-located ground receivers that independently form short-baselines and zero-baselines, the IMs are determined for each receiver for all tracked satellites and then for each satellite differenced for each baseline to evaluate their calibration errors. As first derived from the short-baseline analysis, the effects of calibration errors on IMs range, in total electron content units, from 1.58 to 2.16, 0.70 to 1.87, and 1.13 to 1.56 for GPS, Galileo, and BDS, respectively. Additionally, for short-baseline experiment, it is shown that the code multipath effect accounts for their main budget. Sidereal periodicity is found in single-differenced (SD) IMs for GPS and BDS geostationary satellites, and the correlation of SD IMs over two consecutive days achieves the maximum value when the time tag is around 4?min. Moreover, as byproducts of zero-baseline analysis, daily between-receiver DCBs for GPS are subject to more significant intra-day variations than those for BDS and Galileo. 相似文献