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121.
Oleg I. Yakovlev Yuri V. Pisanko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):552-566
Data from coronal radio-sounding experiments carried out on various interplanetary spacecraft are used to derive the empirical radial dependence of solar wind velocity and density at heliocentric distances from 3 to 60 solar radii for heliolatitudes below 60° and for low solar activity. The radial dependencies of solar wind power and acceleration are derived from these results. Summaries of the radial behavior of characteristic parameters of the solar wind turbulence (e.g., the spectral index and the inner and outer turbulence scales), as well as the fractional density fluctuation, are also presented. These radio-sounding results provide a benchmark for models of the solar wind in its acceleration region. 相似文献
122.
《中国航空学报》2019,32(11):2395-2407
A series of wind tunnel tests were performed to investigate the effect of turbulent inflows on the aerodynamic characteristics of the unsymmetrical airfoil at various turbulence intensities and Reynolds number. To assess the aerodynamic characteristics, surface pressure measurements were made over the unsymmetrical airfoil surface by using a simultaneous pressure scanner MPS4264 of Scanivalve make. Self-generated passive grids made of parallel arrays of round bars were placed at four different locations to generate various Turbulence Intensities (TI) in the wind tunnel. The location of the passive grid has been normalized in terms of considering the distance between the entry of the test section and the leading edge of the model. Based on the wind tunnel results, by comparing the baseline without grid low turbulence case TI = 0.51% with other turbulence generated cases like TI = 4.68%, 4.73%, 6.04% and 8.46% at different Reynolds number, it is found that the coefficient of lift increases with the increase in the turbulence intensity. Results also reveal that the flow featuring turbulence can effectively delay the stall characteristics of an airfoil by attaching the flow over the airfoil for an extended region. Additionally, attempts were made to understand the influence of turbulence on the aerodynamic hysteresis. 相似文献
123.
翼型近尾迹流动的PIV研究—动力学机制 总被引:1,自引:1,他引:0
利用在线式互相关PIV(ParticleImageVelocimetry)系统,在低速风洞中对NACA0012翼型在雷诺数2.39×105,0°和4°攻角下的近尾迹流动进行了详细测量。实验结果表明,翼型近尾迹存在有序的涡街结构,涡街在尾缘处形成后,在向下游的迁移中,会经历一个发展壮大、失稳破碎的演化过程,流动从有序走向无序。翼型的近尾迹是一种以旋涡的运动学特性和动力学机制为主导的流动现象。本文着重探讨了翼型尾缘处的涡街形成机理,尾迹内的流动机制,以及近尾迹的流动稳定性。 相似文献
124.
A.K. Singh Sandhya Mishra Raghvendra Singh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Waves in the Ultra Low Frequency (ULF) band owe their existence to solar wind turbulence and transport momentum and energy from the solar wind to the magnetosphere and farther down. Therefore an index based on ULF wave power could better characterize solar wind–magnetosphere interaction than KP, Dst, AE, etc. indices which described mainly quasi-study state condition of the system. We have shown that the ULF wave index accurately characterize relativistic electron dynamics in the magnetosphere as these waves are closely associated with circulation, diffusion and energization of relativistic electrons in the magnetosphere. High speed solar wind streams also act as a significant driver of activity in the Earth’s magnetosphere co-rotating interaction region and are responsible for geomagnetic activities. In the present paper, we have analyzed various cases related with very weak (quiet) days, weak days, storm days and eclipse events and discussed the utility of the ULF wave index to explain the magnetospheric dynamics and associated properties. We have tried to explain that the ULF wave index can equally be useful as a space weather parameter like the other indices. 相似文献
125.
一枚Chaff火箭在87.4km高度测量到高达0.33s-1的风切变剖面,相信这个切变值是中层大气曾经测量到的最大切变值.在这个异常大风切变层内,垂直速度扰动谱在浮力子区,惯性子区,和粘性子区有谱斜率-3.10,-1.65,和-7.11,这个观测与中性密度扰动一致.计算的内尺度和浮力尺度与扰动谱中的崩溃点不一致,这个结果与中性密度扰动不一致.讨论了湍流和重力波之间的关系,结果表明,增强湍流与波场饱和有好的联系. 相似文献
126.
127.
在吸气式风洞上对两种不同内部流动结构的单层多孔层板进行了流阻实验,采用沿程阻力关系式得出了其流阻特性。应用软件FLUENT,采用隐式有限体积法求解Navier—Stokes雷诺时均湍流方程,对层板冷却结构的内部流动进行了数值模拟,湍流模型采用Realizable κ-ε双方程模型,近壁处湍流利用壁面函数法处理,采用SIM—PLE算法求解速度与压力的耦合。计算表明,层板内部流场结构十分复杂,射流冲击后在扰流柱前反卷形成驻涡。层板结构内部存在流速很低的区域。计算得出的流阻特性与实验结果进行了比较,两者符合较好。 相似文献
128.
129.
采用3种紊流模型来封闭N-S方程,它们分别是标准的K-ε两方程模型;发展的隐式K-ε两方程模型和基于RNG方法的紊流模型。与标准的K-ε两方程模型相比,发展的K-ε两方程模型通过在紊流耗散率方程中增加一项,来说明若干时间尺度,以提高对壁面附近流动的预测能力;基于RNG方法的紊流模型在紊流耗散率方程中增加一项R,能较好地体现大剪切率所产生的强烈的各向异性效应及非平衡效应。应用3种紊流模型对三维压气机叶栅通道紊流流动进行数值分析,并与实验数据比较,结果表明,采用后两种紊流模型计算得到的值与实验数据更接近。 相似文献
130.
《中国航空学报》2016,(5):1247-1261
A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux rang-ing from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophys-ical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction per-formance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport (SST) and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties: density, viscosity, thermal conductivity and specific heat. For very large buoyancy-influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models. 相似文献