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991.
In order to investigate the flow characteristics of swirl injectors for gelled propellants, which actually behaved as non-Newtonian power-law fluid, a swirl axisymmetric model was established to solve Navier-Stokes equations and VOF (volume of fluid) equation, and the power-law constitutive equation was used to describe the rheology characteristics of the gelled propellants. The film thickness and velocity distribution in the swirl injector under different flow conditions were studied numerically. The simulation results show that the increased geometry characteristic parameter of the swirl injector contributes to the decrease of liquid film thickness. The liquid film thickness is almost independent of the pressure drop. The rheologic parameters have great influences on the inner flow of swirl injector: by increasing the fluid consistency index K and power index n, both the axial and the swirl velocities decrease dramatically; higher fluid consistency index K and power index n make the liquid film thickness increase. When the viscosity is large enough, the air core in the injector would vanish. 相似文献
992.
993.
ZHANG Mana FU Zhenbob LIN Yuzhenb LI Jibaoa aAVIC Commercial Aircraft Engine Co. Ltd. Shanghai China bNational 《中国航空学报》2012,25(6):854-863
Air worthiness requirements of the aircraft engine emission bring new challenges to the combustor research and design. With the motivation to design high performance and clean combustor, computational fluid dynamics (CFD) is utilized as the powerful design approach. In this paper, Reynolds averaged Navier-Stokes (RANS) equations of reactive two-phase flow in an experimental low emission combustor is performed. The numerical approach uses an implicit compressible gas solver together with a Lagrangian liquid-phase tracking method and the extended coherent flamelet model for turbulence-combustion interaction. The NOx formation is modeled by the concept of post-processing, which resolves the NOx transport equation with the assumption of frozen temperature distribution. Both turbulence-combustion interaction model and NOx formation model are firstly evaluated by the comparison of experimental data published in open literature of a lean direct injection (LDI) combustor. The test rig studied in this paper is called low emission stirred swirl (LESS) combustor, which is a two-stage model combustor, fueled with liquid kerosene (RP-3) and designed by Beihang University (BUAA). The main stage of LESS combustor employs the principle of lean prevaporized and premixed (LPP) concept to reduce pollutant, and the pilot stage depends on a diffusion flame for flame stabili-zation. Detailed numerical results including species distribution, turbulence performance and burning performance are qualita-tively and quantitatively evaluated. Numerical prediction of NOx emission shows a good agreement with test data at both idle condition and full power condition of LESS combustor. Preliminary results of the flame structure are shown in this paper. The flame stabilization mechanism and NOx reduction effort are also discussed with in-depth analysis. 相似文献
994.
995.
Fabrication of the surface micro-texture on the C-plane sapphire is undertaken by a355 nm Ultraviolet(UV) pulsed laser. The surface micro-textures of sapphire with different laser scanning line spacing ranging from 10 lm to 100 lm are obtained, where the selection range of scanning line spacing is controlled in the range of the groove width and plasma width to obtain a surface of high Peak-Valley(PV) value. A reasonable processing order is proposed to manufacture different types of surface micro... 相似文献
996.
复合材料自动铺带技术——曲面铺带CAM技术 总被引:1,自引:0,他引:1
以自行研制的10轴龙门式自动铺带机为研究对象,建立铺带机的机构数学模型,基于D-H法求解运动学问题;根据数控技术原理并结合铺带机的工作特点,制定相应的数控代码;基于Visual C++6.0平台开发了曲面铺带数控代码生成系统,具有文件读取、参数设定、指令生成等功能和友好的人机交互界面. 相似文献
997.
20世纪90年代以来,中国的国际收支持续顺差,外汇储备已跃居世界第一位,至2007年外汇储备高达1.9万亿美元.通过国际收支平衡表,可以发现中国国际收支的结构特征和外汇储备的变动状况,以及发展趋势存在的问题,进而提出解决的建议. 相似文献
998.
999.
Ying Xiao Qian Wang Mu-Ling Xu Jin-Chang Jiang Bing Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The geomagnetic field (GMF) is one of the essential characteristics of the terrestrial environment but does not apply in outer space. The elimination of GMF may interfere with the normal activities of life in many aspects. Previous behavioral experiments have found that long-term memory is impaired in chicks incubated in a near-zero magnetic environment (i.e. hypomagnetic field or HMF). The present study was designed to evaluate the possible involvement of noradrenergic change in the functional abnormality observed before. A HMF space was produced by nullifying the natural GMF with three pairs of Helmholtz coils. The one-trial passive avoidance learning paradigm was performed on day-old chicks incubated in either the HMF space or the natural GMF. Exogenous noradrenaline was administered by intracerebral injections and the effect on memory consolidation was compared between the two categories of subjects. In the behavioral paradigm, the HMF chicks had a higher elimination rate than the GMF chicks and displayed a significant reduction in overall responsiveness. The administration of moderate doses (0.1–0.5 nmol/hemisphere) of noradrenaline led to fairly good memory retention in GMF chicks but had little effect on HMF chicks. However, long-term memory of HMF chicks could be elevated to the normal level by much higher doses (1.0–1.75 nmol/hem) of the drug. These results suggest that prolonged exposure to HMF may induce disorders in the noradrenergic system in the brain and indicate a potentiality of counteracting the ill-effect of GMF deprivation with appropriate pharmacological manipulation. 相似文献
1000.