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.      

Gravity waves and wind-shear in the MLT at 23°S

We have used the technique suggested by Hocking [Hocking, W. A new approach to momentum flux determinations using SKiYMET meteor radars. Ann. Geophys. 23, 2005.] to derive short period wind variances in the 80–100 km region from meteor radar data. We find that these fluctuating winds, assumed to correspond to gravity waves and turbulence, are closely correlated with the vertical shear of the horizontal tidal winds. This close correlation suggests that in situ wind shear may be a major source of gravity waves and turbulence in the MLT. If this is the case, gravity waves generated in the troposphere and propagating up to the MLT region, generally assumed to constitute an important influence on the climatology of the region, may be a less important source of energy and momentum in the 80–100 km region than has been hitherto believed.     

Prediction of horizontal gas–solid flows under different gravitational fields

In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.     

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.     

基于流动沸腾气泡脱落行为的重力无关性分析

在流动沸腾现象中，气液两相密度差异导致重力对流动和传热性能产生很大影响，因此重力效应研究对于流动沸腾的航天应用具有重要意义.在对Bower-Klausner-Sathyanarayan重力无关准则（BKS准则）分析的基础上，提出其判据存在理论缺陷，不能正确反映重力效应.采用与BKS准则相同的气泡脱落模型，但忽略气泡沿加热管壁的滑动效应，重新计算常重力条件下不同流动方向起始沸腾阶段单气泡的脱落尺寸，归纳得到一个新的基于Fr（Froude数）的重力无关准则.该准则与实验结果符合更好，且与主导作用力准则基本相符.      

New index of long-term variations of galactic cosmic ray intensity

We find that the soft rigidity spectrum of the Galactic Cosmic Ray (GCR) intensity variations for the maximum epoch and the hard rigidity spectrum for the minimum epoch calculated based on the neutron monitors experimental data (1960–2002) are related with the various dependence of the diffusion coefficient on the GCR particle’s rigidity for different epoch of solar activity. This dependence is stronger in the maximum epoch than in the minimum epoch of solar activity, and is provided by the essential temporal rearrangements of the structure of the Interplanetary Magnetic Field (IMF) turbulence from the maxima to minima epoch of solar activity. We also show that the rigidity spectrum of GCR intensity variations is harder for the effective rigidities ∼(10–15) GV (by neutron monitors data), than for the effective rigidities ∼(25–30) GV (by neutron monitors and muon telescopes data). A general scenario of GCR modulation versus solar activity is settled on the essential temporal rearrangements of the structure of the IMF turbulence. Therefore, the temporal changes of the power law rigidity spectrum exponent can be considered as a vital (new) index to explain the 11-year variations of the GCR intensity. We assume that ∼(70–80)% of the changes of the amplitudes of the 11-year variations of GCR intensity is related with the changes of the IMF turbulence versus solar activity.     

不同重力条件下单气泡池沸腾现象的数值研究

对不同重力条件下常压饱和水中单气泡池沸腾现象的气泡生长过程及传热特性进行了数值模拟. 采用简化的润滑流模型计算生长气泡底部微液膜的贡献, 而其他宏观区域的气液两相介质则用连续界面模型统一处理. 气液界面形状和加热面上接触线的运动分别采用Level Set方法和固定的表观接触角来近似刻画. 计算结果表明, 气泡生长过程中, 当量直径近似与生长时间的1/3～1/2次方成正比, 重力对相关趋势的影响不大, 但强烈影响着气泡脱落直径和生长时间, 其中脱落直径反比于重力的1/3次方, 生长时间反比于重力的4/5次方. 在固定的核化点数密度条件下, 加热面平均热流密度近似与壁面过热度的3/2次方成正比, 该趋势并不随重力的减弱而改变.      

Energy dependence of the rigidity spectrum of Forbush decrease of galactic cosmic ray intensity

We show that rigidity spectrum of Forbush decrease (Fd) of galactic cosmic ray (GCR) intensity in September 9–23, 2005 clearly depends on energy. We calculated rigidity spectrum of the Fd based on the neutron monitors and Nagoya muon telescope channels’ data divided in three groups according to their cut off rigidities. We found that temporal changes of rigidity spectrum exponent γ are approximately similar for all cut off rigidity groups, but γ values are the larger the higher are cut off rigidities. We conclude that rigidity spectrum of Fd is hard for lower energy range and is soft for the higher energy range. We believe that an energy dependence of the power law rigidity spectrum of Fd is observed owing to the preferential convection–diffusion mechanism during Fd in September 9–23, 2005. It is a reflection of an influence of the temporal changes of the structure of the interplanetary magnetic field (IMF) turbulence in different range of frequency f during Fd. Particularly, a decisive role in formation of the character of the rigidity spectrum belongs to the changes of the exponent ν of the power spectral density (PSD) of the IMF turbulence (PSD ∝ f^−ν). The exponent ν is greater for high frequency region of the IMF turbulence (responsible for scattering of low rigidity particles of GCR), than for low frequency region of the IMF turbulence (being responsible for scattering of higher rigidity particles). Also, we challenge to estimate an existence of slab/2D structure of solar wind turbulence during the Fd in September 9–23, 2005 based on the distribution of average turbulence energy among the IMF’s components.     

毛细泵回路蒸发器的数值研究

文章针对毛细泵回路(CPL)蒸发器内的多孔芯结构, 建立了描述换热和流动的非稳态数值模型。该模型采用焓模型来处理多孔介质内工质的相变问题, 通过分区计算既避免了采用耗时复杂的自适应网格技术又能方便地跟踪汽液界面, 为处理多孔介质中的毛细力带来方便; 在处理流动问题时, 通过对源项的处理考虑了毛细抽力的作用, 体现了毛细抽力是CPL的动力源, 从给定的算例来分析, 该数值模型较好地反映了毛细芯的工作特性。     

使用Gao-Yong湍流方程计算翼体角偶流动

Gao-Yong湍流方程基于侧偏统计平均方法保留了湍流脉动量的一阶统计信息,并引入加权漂移速度对称性及正交各向异性,导出漂移流连续方程、动量方程和机械能方程,最后依据湍流物理的唯象论,使用动量传输链概念模化封闭了整个方程组.大量算例验证了此方程对广泛范围的复杂湍流问题的适定性.为了进一步的工程应用,将其加入开源计算流体力学软件OpenFOAM(Open Field Operation and Manipulation)中,并就翼体角偶流动进行了数值模拟.翼体角偶流动具有三维分离、马蹄涡等十分复杂的流动特征,通过与实验测量结果的对比研究表明,Gao-Yong湍流方程不论在定性还是定量上,都成功捕捉到这类复杂流动现象的主要特征,得到了令人满意的结果.     

双体小行星系统平衡态与稳定性研究

由于双体小行星独特的运动形式可为行星的演化提供重要线索,因而成为小行星探测中的热点目标。基于双椭球体模型研究了双小行星系统的相对运动、平衡态及稳定性。首先基于双椭球的全二体模型建立了双星系统相对运动的动力学方程;其次利用拉格朗日方程,通过求解系统角动量和能量,建立了双星系统平衡态对应的状态约束;最后给出了通过零速度状态曲面判断双星系统平衡态稳定性的一般性方法,在此基础上分析了小行星物理参数变化对系统平衡态稳定性的影响。研究可为未来双体小行星系统探测任务中的轨道设计与控制提供重要的理论参考。     

质心位置对超空泡射弹尾拍运动影响分析

基于均质平衡流理论,通过求解混合介质的RANS(Reynolds-Averaged Navier-Stokes equations)方程、SST(Shear Stress Transport)湍流方程和不同介质之间的质量输运方程,结合刚体运动方程和网格变形方法,研究了不同质心位置的超空泡射弹尾拍运动特性以及尾拍运动下超空泡形态特性,对比分析了不同质心位置的超空泡射弹尾拍运动的刚体运动和尾拍力的变化特征.结果表明,射弹尾拍运动对空泡形态的对称性有较大影响,发生碰撞处的空泡壁面朝着弹体转动的方向发展;射弹尾拍运动的转动角度、角速度、角加速度以及尾拍阻力和尾拍升力等都表现出周期性变化规律,且随着质心与射弹头部距离的增加,转动惯量增大,变化周期也增大.     

流道弯曲度对微重力膜式水气分离性能的影响

开展微重力膜式水气分离性能仿真研究,对水气分离技术设计与优化具有重要意义。针对微重力入口边界气液界面多尺度问题（入口流型问题）提出了基于界面概率近似方法的欧拉双流体模型,采用动量源项法解决几何多尺度问题（分离膜边界问题）,为仿真研究提供了有效的入口及渗透边界。研究了典型工作参数下流道弯曲度对膜分离性能的影响,并从流动形态和作用力贡献2个方面分析了影响机理。结果表明:膜分离性能随流道弯曲度增大而降低,影响程度与入口含气率相关;直流道适于选作膜式静态水气分离器主要流道形式。      

Perpendicular transport of charged particles: Results for the unified nonlinear transport theory derived from the Newton–Lorentz equation

The perpendicular diffusion coefficient is calculated by combining a recently developed Unified Nonlinear Transport (UNLT) theory with the Newton–Lorentz equation. The total perpendicular mean free path can be described as a combination of a guiding center contribution and a microscopic contribution. It is shown that the total mean free path depends strongly on the energy range of the turbulence power spectrum and on particle energy. Further, a slab/2D composite model is used to investigate the influence of each contribution to the total mean free path for a quasi-3D turbulence model. For pure 2D turbulence the UNLT reduces to the NLGC-theory. For pure slab turbulence the guiding center contribution is subdiffusive in accordance with simulations and the theorem on reduced dimensionality. Conversely, the microscopic contribution is non-zero, which has to be interpreted as normal diffusion.     

Modelling of galactic Carbon in an asymmetrical heliosphere: Effects of asymmetrical modulation conditions

Observations of galactic cosmic rays (GCRs) from the two Voyager spacecraft inside the heliosheath indicate significant differences between them, suggesting that in addition to a possible global asymmetry in the north–south dimensions (meridional plane) of the heliosphere, it is also possible that different modulation (turbulence) conditions could exist between the two hemispheres of the heliosphere. We focus on illustrating the effects on GCR Carbon of asymmetrical modulation conditions combined with a heliosheath thickness that has a significant dependence on heliolatitude. To reflect different modulation conditions between the two heliospheric hemispheres in our numerical model, the enhancement of both polar and radial perpendicular diffusion off the ecliptic plane is assumed to differ from heliographic pole to pole. The computed radial GCR intensities at polar angles of 55° (approximating the Voyager 1 direction) and 125° (approximating the Voyager 2 direction) are compared at different energies and for both particle drift cycles. This is done in the context of illustrating how different values of the enhancement of both polar and radial perpendicular diffusion between the two hemispheres contribute to causing differences in radial intensities during solar minimum and moderate maximum conditions. We find that in the A > 0 cycle these differences between 55° and 125° change both quantitatively and qualitatively for the assumed asymmetrical modulation condition as reflected by polar diffusion, while in the A < 0 cycle, minute quantitative differences are obtained. However, when both polar and radial perpendicular diffusion have significant latitude dependences, major differences in radial intensities between the two polar angles are obtained in both polarity cycles. Furthermore, significant differences in radial intensity gradients obtained in the heliosheath at lower energies may suggest that the solar wind turbulence at and beyond the solar wind termination shock must have a larger latitudinal dependence.     

脉冲射流对环量控制翼型气动性能的影响

定常射流在大迎角下气动性能较差,借助脉冲射流能够有效改善大迎角下的气动性能,并减少射流所需质量流量。采用非定常数值模拟的方法进行了脉冲射流作用下的环量控制翼型气动特性计算和流场分析。总结了占空比和频率分别对时均升力和升力脉动幅值的影响趋势;分析了不同迎角下的脉冲射流流动机理;进一步指出了射流动量系数的影响规律,并借助脉冲射流和定常射流的叠加效应有效缓解了升力脉动现象。结果表明:低占空比、同等升力系数下,脉冲射流可大幅度减小质量流量,但升力脉动幅值较大;小迎角下随频率增大,升力系数先增大后减小,但整体变化幅度不大,大迎角下随频率增大,升力系数持续性增大;脉冲射流能够推迟失速迎角,扩宽环量控制技术的可用迎角,并且随动量系数增大,这种优势更加明显;借助脉冲射流与定常射流的叠加效应,能够有效缓解脉冲射流作用下的升力脉动现象,达到飞行使用条件。      

Satellite orbits in Levi-Civita space

In this paper we consider satellite orbits in central force field with quadratic drag using two formalisms. The first using polar coordinates in which the satellite angular momentum plays a dominant role. The second is in Levi-Civita coordinates in which the energy plays a central role. We then merge these two formalisms by introducing polar coordinates in Levi-Civita space and derive a new equation for satellite orbits which unifies these two paradigms. In this equation energy and angular momentum appear on equal footing and thus characterize the orbit by its two invariants. Using this formalism we show that equatorial orbits around oblate spheroids can be expressed analytically in terms of Elliptic functions. In the second part of the paper we derive in Levi-Civita coordinates a linearized equation for the relative motion of two spacecrafts whose trajectories are in the same plane. We carry out also a numerical verification of these equations.     

挡板对液体推进剂晃动力的影响

研究了全尺度重力探测卫星－Ｂ贮箱对于安装档板和不安装挡板情形下液体推进剂晃动的液体动力特性。结果显示,以重力瞬变加速度和重力梯度加速度为作用力的轨道加速度使液体推进剂产生了晃动,安装挡板使晃动幅度减小。由于推进剂在贮箱中上下运动的同时伴随着左右运动而产生了作用于贮箱上的力,通过液体推进剂与贮箱壁面的应力关系计算了作用在贮箱上的力。计算模拟结果显示,挡板产生的阻尼在减少流体晃恸 的同时也减少了流体作     

翼型波浪水面巡航地面效应数值模拟

数值求解非定常不可压缩流动的雷诺平均N-S(Navier-Stokes)方程和标准k-ε湍流模型,用VOR(Volume Of Fluid)方法模拟波浪水面,模拟了NACA2410翼型在波浪水面上方飞行的流场.研究了余弦波浪水面的生成方法,选取合适的计算网格和时间步长,避免了在生成规则余弦波浪水面时由于数值耗散使波面形状衰减.比较了固壁波浪与水面波浪计算结果的差异,发现固壁波浪的结果更接近余弦曲线分布.研究了波浪等级对翼型气动性能的影响,分析计算结果发现:在规则的余弦水面波浪上方飞行,翼型气动力呈现周期性,给出了一个周期内气动力的变化过程,以及波长和波幅对气动力平均值和波动幅度的影响规律.      

蜻蜓爬升过程间歇性拍动飞行现象的数值研究

采用数值模拟方法研究了蜻蜓双翼做间歇性拍动运动时的气动特征。计算结果表明,在所研究的雷诺数工况下(Re=157),模型翼的平均升力系数和平均推力系数随着间歇占比的增大而减小,前段下降较快,中段下降平缓,后段下降至零。其中平均推力系数受到的影响相对平均升力系数更大,当连续飞行转变为间歇性飞行时,短暂滑翔初期和短暂滑翔稳定阶段均大幅削弱推力系数,共占42.7%;而对于升力系数,短暂滑翔稳定期对升力系数的削弱作用很大,占41.4%,但短暂滑翔初期却对平均升力系数的提高贡献8%。间歇拍动飞行能够提高蜻蜓飞行的升推比,当滑翔时长占间歇飞行周期之比为0.3时,平均升推比接近为1。