Numerical investigation of the influence of large turbulence scales on the parallel and perpendicular transport of cosmic rays

In recent analytical investigations it has been demonstrated that the turbulence behavior at large scales has a very strong influence on the perpendicular diffusion coefficient of charged particles. In the present paper we use computer simulations to investigate numerically cross field transport and particle propagation along the mean magnetic field for different turbulence models at large scales. Our results are compared with quasilinear theory and nonlinear diffusion theories. We show that for different forms of the turbulence spectrum at large scales, the perpendicular mean free paths obtained numerically are in agreement with recent predictions made by analytical theory. It is also shown that the parallel diffusion coefficient contains always a strong nonlinear contribution which is, however, independent of the assumed spectrum at large scales.     

太阳风中动力论Alfven波的湍流谱(a)朗道衰减

提出一个太阳风中Alfven脉动湍流的新模式,动力论Alfven波是Alfven波和离子声波非解耦的新波模。由太阳向外传播的各种波长的动力Alfven波的非线性相互作用推导出动力论Alfven脉动湍流功率谱P_k,在Alfven半径以外,P_k∝k-3/2,而在Alfven半径以内,由太阳附近的P_k∝k-1变化成P_k∝k-3/2动力论Alfven脉动在Alfven半径以内完成朗道衰减。新模式克服了以前理论模式遇到的困难。      

大气紊流数字仿真的改进方法

赵震炎等提出了一种数字摸拟Dryden大气紊流的方法。该方法使用方便,并具有一定的理论基础。但是在某些步长情况下它的相关函数和Dryden模型的理论值吻合得还不够令人满意。本文从理论上分析了产生误差的原因,并且提出了改进的方法。通过相关性检验可以看到改进后的仿真结果非常符合Dryden谱的大气紊流模型。     

近壁区理论耗散率模型的改进

提出了在边界层的近壁区,采用共振三波的理论模型描述湍流边界层相干结构,由此解决了对称三维波理论模型不能处理三阶相关量的问题,根据新的理论模型对ε方程逐项进行计算和分析.与原理论模型计算结果相比,本文理论结果与直接数值模拟(DNS)符合更好.     

近壁区湍能耗散率输运方程的理论模型

提出在湍流边界层的近壁区采用三维不稳定波来描述湍流扰动速度,然后根据理论模型对湍能耗散率的生成、粘性破坏以及扩散等特性进行了系统定量的计算和分析.理论计算结果与直接数值模拟结果符合较好,特别是在y<10的区域中明显优于传统湍流模型的计算结果.这不仅在理论上有益于对湍流物理机制的了解,而且可能为湍流模型计算开辟一条新的途径.     

基于改进多目标遗传算法的舰尾紊流模拟方法

为提高舰尾紊流自由大气紊流分量仿真的可信度,提出了一种紊流数值模拟的新方法.首先,使用带有修正系数的Euler前向差分格式表示各个方向的紊流序列,同时结合智能算法的思想,把紊流相关性检验中的均方差误差和相关函数误差作为待优化目标函数,将修正系数的选择看成一个多目标优化问题,并采用改进的多目标遗传算法进行求解.最后,通过仿真算例验证了本文方法的正确性与合理性,计算结果表明该方法可以根据不同的采样步长灵活地生成所需紊流.尤其在小步长情况下,亦可得到很好符合理论值的紊流序列,可以满足虚拟飞行实验的要求.      

弹性飞机平衡的阵风外载荷计算与分析

连续紊流是适航规范中阵风载荷分析必须考虑的一种阵风模型,但其引起的阵风载荷在飞机结构设计中的应用一直存在困难.在平稳随机过程的假设下,基于von Karman连续紊流功率谱模型和线性系统连续紊流响应的功率谱方法,使用载荷累加法获得外载荷形式的阵风载荷.在此基础上,通过引入载荷响应的相关性推导并建立了一种生成多组连续紊流平衡外载荷分布的方法.垂向连续紊流情况下的算例结果表明:连续紊流外载荷分布是全机平衡的.平衡的外载荷分布可通过机动飞行载荷分析中的载荷包线方法识别载荷设计情况,从而应用于飞机结构的强度分析与设计.     

A Brief Review of Interplanetary Investigations in China from 2014 to 2016

Great progress has been made in the research of solar corona and interplanetary physics by the Chinese scientists during the past two years (2014-2016). Nearly 100 papers were published in this area. In this report, we will give a brief review to these progresses. The investigations include:solar corona, solar wind and turbulence, superhalo electron and energetic particle in the inner heliosphere, solar flares and radio bursts, Coronal Mass Ejections (CMEs) and their interplanetary counterparts, Magnetohydrodynamic (MHD) numerical modeling, CME/shock arrival time prediction, magnetic reconnection, solar variability and its impact on climate. These achievements help us to better understand the evolution of solar activities, solar eruptions, their propagations in the heliosphere, and potential geoeffectiveness. They were achieved by the Chinese solar and space scientists independently or via international collaborations.      

垂直激波条件下能量粒子加速机制的模拟研究

在具有湍动的磁场和垂直激波条件下对大量测试粒子的轨迹进行了数值计算,研究了激波强度和粒子初始能量对于粒子穿越激波的平均能量变化的影响,分析了漂移加速(SDA)在不同条件下对粒子加速的贡献,并给出了一个与数值结果相符合的漂移加速理论公式△E=amvivup(1-1/s).结果表明,加入磁场湍流后,垂直激波条件下粒子仍主要受到漂移加速作用,而基于粒子引导中心的耗散漂移加速理论在此条件下失效.      

微重力量值对气液两相流相分布及液相湍流统计量影响的数值研究

气液两相流在空间领域具有广阔的应用前景, 深入理解微重力量值(微重力大小)对相分布和液相湍流的影响十分必要. 采用欧拉elax-elax拉格朗日双向耦合模型深入研究了不同微重力量值对相分布和液相湍流的影响. 液相速度场通过直接数值模拟求解, 气泡的运动轨迹由牛顿运动方程跟踪. 研究表明, 气泡分布和液相湍流与微重力量值均具有直接联系. 在低微重力量值下, 气泡近似均匀分布在槽道内, 且对液相湍流统计量几乎没有影响; 然而当微重力量值较高时, 大量气泡聚集在壁面附近, 液相湍流由于气泡的注入受到极大调制.      

Bodies in flowing plasmas: Laboratory studies

A brief review of early laboratory investigations of bodies in flowing, rarefied plasmas is given together with a discussion of more recent parametric studies carried out at NASA/Marshall Space Flight Center (MSFC), which include the effects of the ion acoustic Mach number and the normalized test body potential. Good agreement is found between the experimental results and theoretical calculations which omit ion thermal motion. The relation between laboratory investigations and the results of satellite-borne measurements is addressed. This relationship has led to an appreciation for the benefits of applying the methods and techniques of laboratory plasma physics to investigations in space, where several limitations inherent to the laboratory can be circumvented. These types of investigations, conducted in Earth orbit, can enhance our understanding of space plasma physics and have direct application to certain types of solar system phenomena.     

降落伞充气过程研究方法综述

文章介绍了降落伞充气过程的研究方法 ,包括完全试验方法、半试验半理论方法及完全理论方法。其中 ,着重介绍了半试验半理论方法及完全理论方法的内容及发展状况。在介绍各种研究方法的同时 ,阐述了降落伞充气过程包含的复杂物理现象、研究难点及解决方法 ;最后指出了当前充气过程研究的热点及发展趋势。     

近壁区Reynolds应力输运方程的理论模型

在湍流边界层的近壁区,采用对称共振三波的理论模型描述相干结构,根据理论模型对Reynolds应力输运方程逐项进行计算和分析,结果与直接数值模拟符合很好.这不仅在理论上有益于对湍流物理机制的了解,而且展现了一种可能性,即根据相干结构的理论知识来改造湍流模型,使之具有更清晰的物理内涵以提高近壁区的预估精度.     

沟槽面湍流减阻研究综述

对近20年来沟槽面湍流边界层特性、湍流拟序结构、湍流减阻及其机理的研究进展进行了综述.内容涉及沟槽面平板、旋成体、机翼等在压、跨、超音速流动情况下的实验研究成果;压力梯度、攻角、侧滑角等的影响;湍流猝发特性、紊动特性、近壁区带条结构的特征及减阻机理等方面的工作.为更有效地减少表面摩阻,必须深入开展对沟槽面湍流边界层特性、湍流拟序结构及湍流减阻机理等方面的研究.      

Current fluctuations in the Earth''s magnetosphere caused by lower-hybrid-drift turbulence

Nonlinear calculations of the anomalous electrical conductivity in the plasma of the earth's plasma mantle, the tail plasma sheet boundary layer and the ionospheric F-region density-trough are presented provided that lower-hybrid-drift turbulence exists. It is shown that in these regions the stabilization of the wave growth is mainly caused by current relaxation. Further, the fluctuations of the electrical currents are estimated via Ampère's and Ohm's laws. It is found that the lower-hybrid-drift turbulence causes maximum anomalous collision frequencies of the order of 10⁻² Hz in the magnetosphere. The maximum current fluctuations are about 3 10⁻⁹ A/m². The theoretical results are in agreement with ISEE and Prognoz-8 measurements.     

扩压叶栅端壁角区旋涡对湍流特性的影响

为了弄清扩压叶栅端壁角区旋涡对湍流特性分布的影响,用三维激光多普勒测速技术测量了平面扩压叶栅中角区流动的湍流特性.对测量结果的分析表明:流向涡的核心区域及旋涡与附面层相互作用区域的湍流动能增加.同时,旋涡和旋涡运动强烈影响着雷诺正应力和切应力的分布规律.     

Factors influencing the heating of the auroral electrojet by high power radio waves

Results are presented from recent ionospheric modification experiments in which the EISCAT UHF radar measured the E-region temperature and density response to high power RF heating above Tromsø. A variety of electrojet conditions were encountered during these experiments. In particular, the electron drift velocity varied considerably allowing the heating efficiency of the RF heater to be investigated as a function of electron flow velocity. These observations constitute the first direct investigation of electrojet temperature modifications by high power radio waves and provide a test of a recent theoretical model in which the combined effects of RF heating and of natural plasma turbulence associated with the Farley-Buneman instability have been considered.     

Influence of atmospheric turbulence on planetary transceiver laser ranging

In this paper we investigate the influence of atmospheric turbulence on the performance of the uplink of a planetary transceiver laser ranging system using a single photon detector. We numerically combine the influence of turbulence in the mean intensity profile variations, scintillation, beam-wander induced pointing errors and stochastic time-of-flight variations, using the Hufnagel–Valley turbulence profile to model the ground turbulence behavior. We map the intensity variations due to turbulence to variations in the probability distribution of the arrival time of the 1st photon in a laser pulse, which influences the range measurement error probability distribution. The turbulence models are applied to assess the influence on single-pass range accuracy and precision statistics, as well as the parameter estimation quality of a Phobos Laser Ranging (PLR) mission.     

Analysis of the turbulence observed in the outer cusp turbulent boundary layer

One of the prominent features of the cusp Turbulent Boundary Layer (TBL) is a persistent low frequency electromagnetic turbulence that extends from <1Hz up to the electron cyclotron frequency, accompanied by what appears to be purely electrostatic noise above this frequency range. The Plasma Wave Instrument onboard Polar obtained plasma wave measurements in the cusp TBL in the form of waveform captures simultaneously from 6 different sensors (3 each orthogonal electric and magnetic) in the frequency range 1 Hz up to 25 kHz. This allowed us to directly calculate the phase velocity from the measured ratio of |dE| to |dB| and compare it to theoretical values for various modes. Using this technique, we have gained some insight into the mode of the electromagnetic turbulence that extends in frequency from 1 Hz up to the electron cyclotron frequency (several hundred Hz to a few kHz) in the TBL. The whistler and kinetic Alfvén wave modes are discussed as the possible modes of this turbulence. By analyzing the high time resolution waveforms, we isolate and identify some of these modes. The electrostatic turbulence above the electron cyclotron frequency is associated with pulses and quasi-sinusoidal waveforms observed in the measured time series. These do not fit any known mode, although work is continuing in this area to show that some of them may be associated with electron holes or with downshifted Langmuir waves produced through a two-stream instability.     

收缩段出口型式对水槽流场品质的影响

研究了收缩段出口顶壁型式对表面波的影响，得到了最佳的出口设计，并分析了满流和明流情况下，流场速度，湍流等澡程的发展变化。