Aero-optical effects simulation technique for starlight transmission in boundary layer under high-speed conditions

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.     

固体燃料冲压发动机附着点分析与模拟

对固体燃料冲压发动机冷流情况下,由突扩台阶产生的附着点进行了理论分析和数值模拟, 得出附着点与台阶高度成线性关系, 与燃烧室尺寸、壁面是否加质等因素有关, 但与入口空气流量无关, 所得结果与实验数据比较吻合。     

边界层内水介质在压差驱动下沿小孔向气腔射流问题研究

对边界层内小孔气水多相流场下射流问题开展数值仿真及定常水洞试验研究,建立了适用于边界层内压差驱动下小孔向气腔射流多相流场问题研究的数值仿真计算模型,针对典型孔参数及气水流场条件,对比分析了仿真试验数据,验证了数值仿真模型的正确性及模型计算精度。结合流体质点受力及运动模型及平板边界层理论,分析了气水域压力场特征及水域流动规律对小孔射流过程的作用机理及影响规律,开展了孔参数对射流多相流场特征及射流量的影响研究。获得了小孔射流量估算方法,为航行体上防水装置设计提供数据支撑。     

基于矩谐分析的高精度局部地磁场建模研究

高精度地磁基准图的绘制是实现地磁导航的关键。本文论述了应用矩谐分析方法进行地磁场     

边界元法计算厚板表面裂纹问题的应力强度因子

建立了一种能反映裂纹尖端应力、应变奇异性的三维等参奇性边界元，应用边界元分析方法求得了具有半椭圆形和半圆形表面裂纹厚板的应力强度因子。结果表明，采用这种计算方法得到了满意的计算效果。     

Linear stability analysis of interactions between mixing layer and boundary layer flows

The linear instabilities of incompressible confluent mixing layer and boundary layer were analyzed.The mixing layers include wake,shear layer and their combination.The mean velocity profile of confluent flow is taken as a superposition of a hyperbolic and exponential function to model a mixing layer and the Blasius similarity solution for a flat plate boundary layer.The stability equation of confluent flow was solved by using the global numerical method.The unstable modes associated with both the mixing and boundary layers were identified.They are the boundary layer mode,mixing layer mode 1 (nearly symmetrical mode) and mode 2 (nearly anti-symmetrical mode).The interactions between the mixing layer stability and the boundary layer stability were examined.As the mixing layer approaches the boundary layer,the neutral curves of the boundary layer mode move to the upper left,the resulting critical Reynolds number decreases,and the growth rate of the most unstable mode increases.The wall tends to stabilize the mixing layer modes at low frequency.In addition,the mode switching behavior of the relative level of the spatial growth rate between the mixing layer mode 1 and mode 2 with the velocity ratio is found to occur at low frequency.     

高温环境下硅酸铝纤维的隔热性能

　硅酸铝纤维供应商往往只提供客户硅酸铝纤维在某一温度的热导率,难以指导隔热结构的设计。

本文针对市场上常用的硅酸铝纤维板,设计了隔热性能测试装置,实验获得硅酸铝纤维温度随时间的变化曲

线,并进行了有限元仿真分析。研究表明,硅酸铝纤维隔热效果稳定且具有一定的抗热辐射能力。有限元分析

结果与实验数据基本一致,说明采用有限元分析方法能够支持设计人员较好预测隔热效果。

     

High-Latitude Particle Precipitation and its Relationship to Magnetospheric Source Regions

Two central issues in magnetospheric research are understanding the mapping of the low-altitude ionosphere to the distant regions of the magnetsphere, and understanding the relationship between the small-scale features detected in the various regions of the ionosphere and the global properties of the magnetosphere. The high-latitude ionosphere, through its magnetic connection to the outer magnetosphere, provides an important view of magnetospheric boundaries and the physical processes occurring there. All physical manifestations of this magnetic connectivity (waves, particle precipitation, etc.), however, have non-zero propagation times during which they are convected by the large-scale magnetospheric electric field, with phenomena undergoing different convection distances depending on their propagation times. Identification of the ionospheric signatures of magnetospheric regions and phenomena, therefore, can be difficult. Considerable progress has recently been made in identifying these convection signatures in data from low- and high-altitude satellites. This work has allowed us to learn much about issues such as: the rates of magnetic reconnection, both at the dayside magnetopause and in the magnetotail; particle transport across the open magnetopause; and particle acceleration at the magnetopause and the magnetotail current sheets.     

Observational Evidence for Transfer of Plasma Across the Magnetopause

There is a long history of particle measurements that have established that plasma is being transferred across Earth's magnetopause in both directions. The paper reviews the nature of the observational evidence as well as the implications regarding the transfer mechanisms and their efficiencies.     

ISEE Ion Composition Data with Implications for Solar Wind Entry into Earth's Magnetotail

Energetic (0.1-16 keV/e) ion data from a plasma composition experiment on the ISEE-1 spacecraft show that Earth's plasma sheet (inside of 23 RE) always has a large population of H+ and He++ ions, the two principal ionic components of the solar wind. This population is the largest, in terms of both number density and spatial thickness, during extended periods of northward interplanetary magnetic field (IMF) and is then also the most "solar wind-like" in the sense that the He++/H+ density ratio is at its peak (about 3% on average in 1978 and 79) and the H+ and He++ have mean (thermal) energies that are in the ratio of about 1:4 and barely exceed the typical bulk flow energy in the solar wind. During geomagnetically active times, associated with southward turnings of the IMF, the H+ and He++ are heated in the central plasma sheet, and reduced in density. Even when the IMF is southward, these ions can be found with lower solar wind-like energies closer to the tail lobes, at least during plasma sheet thinning in the early phase of substorms, when they are often seen to flow tailward, approximately along the magnetic field, at a slow to moderate speed (of order 100 km s-1 or less). These tailward flows, combined with the large density and generally solar wind-like energies of plasma sheet H+ and He++ ions during times of northward IMF, are interpreted to mean that the solar wind enters along the tail flanks, in a region between the lobes and the central plasma sheet, propelled inward by ExB drift associated with the electric fringe field of the low latitude magnetopause boundary layer (LLBL). In order to complete this scenario, it is argued that the rapid (of order 1000 km s-1) earthward ion flows (mostly H+ ions), also along the magnetic field, that are more typically the precursors of plasma sheet "recovery" during substorm expansion, are not proof of solar wind entry in the distant tail, but may instead be a time-of-flight effect associated with plasma sheet redistribution in a dipolarizing magnetic field.