重力跳动对多相流体系统的影响

研究了重力跳动对液桥表面及内部流体流动的影响, 以期明确重力跳动对多相流体系统的作用效果. 理论研究表明, 当重力跳动作用于液桥时, 液桥反响频率的大小取决于液桥尺寸和物性参数; 实验研究显示重力跳动引入的液桥表面振动、液桥内部流动与温度振动之间存在着三角耦合关系; 数值模拟结果揭示了重力跳动作用于液桥时液桥内部流体的流动结构. 另外, 对理论、实验与数值模拟结果进行了对比验证, 得到了吻合一致的结果.      

Equatorial planetary waves in the mesosphere observed by airglow periodic oscillations

Planetary scale waves in the equatorial upper mesosphere were studied by measuring the airglow OI557.7 nm, O₂b(0,1) and OH(6,2) emission intensities and OH rotational temperature at São João do Cariri (7.4°S; 36.5°W). From four years of data, 1998–2001, periodic oscillations of the airglow emissions were analyzed using the Lomb–Scargle spectral analysis. An oscillation of 3–4 days was frequently observed, which might be ultra-fast Kelvin waves. No seasonal dependency of the wave activity was found. On some occasions we found a quasi-5-day oscillation with a phase difference between the emissions, suggesting an upward energy flow. This is interpreted as a normal mode Rossby wave.     

低热层臭氧含量振荡和温度起伏间的耦合关系

本文求出了声重波传播过程中,低热层臭氧含量振荡和温度场起伏间的耦合关系。首次揭示出其正负相关性的内在原因和判据——动力扰动尺度。在中小尺度声重波扰动范围内,臭氧含量振荡与温度场起伏是正相关的,且相关幅度可达或超过7;而在大尺度或行星尺度波范围内,则一般为负相关。此发现可解释低热层中臭氧含量快速变化及臭氧含量长时间纬圈平均值变化与温度场成负相关的观测事实。本文还在声重波尺度范围内比较了线性和非线性理论的结果,结果表明两者没有太大的差异。     

航天遥感器用泵驱两相流体回路热真空试验研究

针对航天遥感器核心组件的高精度与高稳定度的控温需求,设计并搭建了一套泵驱两相流体回路(MPTL)试验装置,该装置使用了一套具有被动冷却能力的两相控温型储液器。为验证MPTL系统在高真空、极低温与变化外热流条件下的工作能力,在真空罐内对MPTL系统在不同工况点下的散热与控温能力进行了测试,并通过温度和压力等数据研究了主回路的运行特性、储液器内热力学变化特性及两者之间的传热传质过程。结果表明：MPTL系统的控温点可通过储液器进行快速调整,蒸发器温度的变化受外热流与热源开关影响较小;进入毛细管中的过冷液与储液器中的液相形成的温差保证了储液器冷量的供应;主回路发生相态转变时,储液器与主回路工质交换特性引起了系统压力降脉动。     

Long-period wave signatures in mesospheric OH Meinel (6,2) band intensity and rotational temperature at mid-latitudes

A high performance imaging system has been used to investigate the signature of long-period, ∼8-hr, wave-like oscillations evident in the OH Meinel (6,2) band emission (peak altitude ∼87 km) during the fall and early winter months. The measurements were made from two mid-latitude sites in the western USA during 1996/7. Previous investigations of the induced temperature perturbations (amplitude and phase) suggest that many of these events exhibit characteristics akin to the mid-latitude terdiurnal tide (Pendleton, 2000). To further investigate the origin of these waves we have performed an initial investigation using the Krassovsky ratio (η) method, to determine the amplitude ratio of the induced perturbations in the zenith OH emission intensity and rotational temperature and to study their phase relationship (φ). A range of values for the magnitude and phase of η were found with a mean value of |η| = 6 ± 2 (range ∼2–10), and φ = −51° ± 21° (range −11° to −94°) with the temperature perturbation always leading the intensity wave. These results are in good agreement with existing high-latitude studies of distinct 8-hr oscillations in the literature. However, comparison with realistic gravity wave and terdiurnal tidal model computations reveal a conflicting situation where the observed negative phase results point more towards a long-period gravity wave interpretation rather than a terdiurnal tide.     

贮箱内低温推进剂汽化过程的CFD数值仿真

为研究贮箱内低温推进剂相变对推进剂温度和贮箱压力的影响,对贮箱内的传热传质过程进行了仿真.仿真涉及的物理过程包括贮箱与外界环境的换热、推进剂的自然对流、推进剂与贮箱内壁面的换热以及低温推进剂的相变过程等.根据热力学平衡原理建立了低温推进剂相变模型,使用CFD(Computational Fluid Dynamic)方法对处于地面常压停放状态的液氢贮箱进行了450 s的仿真.研究表明随着贮箱壁面传热过程的稳定,推进剂的温度分布、流动状态以及相变情况会趋于稳定;通过仿真获得了推进剂单位时间的汽化量;影响相变的主要因素是贮箱壁面漏热以及推进剂自身的对流运动.     

两相流气体种类灭B类火效果的实验

两相流灭火系统中,气相采用不同的气体,其灭火效果不同.研究了采用空气、氮气、二氧化碳、氩气4种不同种类气体条件下,两相流细水雾灭火系统在3.6 m×4.6 m×3.9 m的空间内,灭0.1 MW及0.61 MW方油盘火的灭火特性及规律.实验过程中采用热电偶树和西门子气体分析仪对火焰温度及火场氧体积分数进行了测量,得到了不同气体种类条件下的细水雾灭火特性包括火焰最高温度、温度下降速率、氧体积分数下降速率、灭火时间等参数的变化规律和灭火过程中火场温度场和氧体积分数值的变化规律.     

Thermocapillary-driven convection in supported and floating-zone crystallization

Marangoni flow was induced in a thin disk of molten tin with an atomically clean surface by heating it from below in an ultra high vacuum apparatus. The radial distribution of temperature was measured and no temperature oscillations were observed. Strong mechanical disturbances introduced at a Marangoni number of about 4300 died out quickly with time indicating that the system was stable. Mathematical models indicate that strong flows in a two cell structure exist under the conditions studied, and that the velocity profile in the cell near the surface is of the bouindary layer type which varies rapidly with depth.     

Melt temperature fluctuations: Causes and response of the solidification front

It is well understood that temperature oscillations and fluctuations during melt growth give rise to fluctuating concentration of solute in the crystal — so-called solute (or impurity) striations. A major source of the temperature fluctuations is the transition to turbulence in the melt resulting from strong buoyancy and/or surface-driven flows. The interaction of these natural convective flows with any imposed rotation is of significance. The major factors causing flow transitions and particularly those which lead to time-dependent flows in Czochralski and float-zone melts will be briefly reviewed and the likely influence of a low-g environment considered. Theoretical analysis and experimental study of the response of the crystal-melt interface to such temperature fluctuations is reviewed and criteria for maximising crystal homogeneity discussed.     

Conditions for the onset of temperature oscillations in a simulated floating-zone configuration

The floating-zone method for crystal growth is studied in simulated low-gravity conditions by suspending a drop of fluid vertically between two circular rods and heating the upper rod with a heater. Flow and temperature oscillations are observed under certain conditions. The temperature oscillation level and the oscillation frequency are measured against the Marangoni number for several aspect ratios using hexadecane and Fluorinert as the test fluids. It is observed that, contrary to what has been believed, the Marangoni number is not the proper parameter to describe the onset of oscillation.     

Alfvén gravity waves in viscous solar plasma: Effect of the background flow

We study the Propagation and damping properties of Alfvén gravity waves in the presence of the vertical magnetic field in the viscous solar plasma under influence of the background flow by deriving a fourth order dispersion relation in terms of the Doppler shifted frequency. We derive the dispersion relation under WKB and Boussinesq approximation. We study the damping of Alfvén gravity waves for the wave frequencies less than and greater than the Brunt-Väisälä frequency. We find that the Brunt-Väisälä frequency divides the frequency ranges where the weakly or strongly damped oscillations occur. The background flow exhibits a strong effect on weakly damped oscillations and a weak effect on the strongly damped oscillations. We also notice that the damping of both the strong and weakly damped oscillations depend on the Brunt-Väisälä frequency and wave number. The effect of the background flow is also being governed by the Brunt-Väisälä frequency and wave number. We also study the properties of gravity wave mode after filtering the Alfvén wave mode by minimizing the magnetic field and noticed that the background flow shows a very strong effect on the gravity wave mode.     

平板型MLHP温度波动研究

环路热管(Loop Heat Pipe,LHP)是一种靠蒸发器的毛细芯产生毛细力驱动回路运行,利用工质相变来传递热量的高效传热装置。研制了一套平板式蒸发器、风冷式冷凝器的小型环路热管(MLHP),MLHP的毛细芯为500目不锈钢丝网,工质为丙酮,蒸发器、冷凝器以及所有管路均由紫铜制成。主要研究了平板型MLHP在不同热负荷条件下的温度波动特性,并重点研究了倾角以及充灌量等对MLHP系统温度波动的影响,且给出相应的合理解释。实验结果表明,平板式MLHP在2~3W/cm2热流密度区间范围内容易发生温度波动。     

Plasma sheet oscillations and their relation to substorm development: Cluster and double star TC1 case study

We examined two consecutive plasma sheet oscillation and dipolarization events observed by Cluster in the magnetotail, which are associated with a pseudo-breakup and a small substorm monitored by the IMAGE spacecraft. Energy input from the solar wind and an associated enhancement of the cross-tail current lead to current sheet thinning and plasma sheet oscillations of 3–5 min periods, while the pseudo-breakups occur during the loading phase within a spatially limited area, accompanied by a localized dipolarization observed by DSP TC1 or GOES 12. That is, the so-called “growth phase” is a preferable condition for both pseudo-breakup and plasma sheet oscillations in the near-Earth magnetotail. One of the plasma sheet oscillation events occurs before the pseudo-breakup, whereas the other takes place after pseudo-breakup. Thus there is no causal relationship between the plasma sheet oscillation events and pseudo-breakup. As for the contribution to the subsequent small substorm, the onset of the small substorm took place where the preceding plasma sheet oscillations can reach the region.     

Venus atmospheric platform options revisited

Various balloon systems intended as scientific platforms to float in the atmosphere of Venus at altitudes between about 35 and 65 km are briefly reviewed. Previous predictions of the altitude oscillations of balloons filled with helium gas and water vapor are largely confirmed through numerical simulation and analysis. The need for refined thermal modelling is emphasised. Several novel technical concepts are introduced. It is concluded that phase change balloons would be more suitable than non-condensing super pressure gas balloons when repeated altitude excursions are a mission requirement.     

基于Fluent的电液泵流场与温度场有限元分析

介绍三相异步电机-轴向柱塞式电液泵(EHP)的集成结构与工作原理,计算电液泵机械损耗,在Ansoft软件中建立电液泵电机模型,仿真分析电液泵的电磁损耗,并在此基础上建立有限元耦合模型,借助Fluent软件仿真分析液压油在壳体内腔的流动与温度分布状态,以及关键零部件的温度分布。有限元分析结果表明,液压油可以在流道内充分流动,并且额定工作状态下,当进口液压油温度为35℃时,电机定子最高温度不超过58℃,转子最高温度不超过40℃,散热效果好于传统电动机-泵组。针对定子内部温度较高的现象,研究了定子四周打4个直径10 mm的通孔后的温度分布情况,并与打孔前进行了对比,结果表明,打孔后电机定子最高温度降低了0.6℃,局部区域温度降低超过3℃,散热效果改善明显。     

赤道异常的行星波周期振荡的统计特征与逐年变化及其QBO调制

利用赤道异常峰区台站(Okinawa)观测的, f₀F₂资料(1977—1990), 分析计算了赤道电离层行星波周期振荡(2日、3—4日、5—7日及10—16日)的特征及其变化规律, 发现其在一年四季都有出现, 但相对强度在冬、夏季较大, 且冬季更强;其振荡周期也随季节有所变化, 以2日波而言, 夏季更接近于2日, 而冬季则多在2日多至2日半区间振荡;更长周期的波的所谓夏季峰值的出现, 还有向夏初和夏末过渡的趋势。并发现振荡与太阳活动性呈负相关, 即低年的相对幅度要强于高年, 并且周期越长负相关越显著;同时显示出振荡的出现率及频率变化受到QBO的调制, QBO东风相期间比西风相更易于出现长周期振荡。这些结果说明赤道电离层明显受到中低层大气动力学变化的向上耦合的影响。      

Numerical simulations of water spray on flame deflector during the four-engine rocket launching

This paper aims to study on the cooling effect with two types of water spray nozzle on the flame deflector during the four-engine launch vehicle take-off. To accurately simulate the two-phase flow of the rocket gas with multispecies and the water spray, the three-dimensional compressible Navier-Stokes equations, discrete ordinates methods and realizable k-Ɛ turbulence model are used to establish the rocket supersonic plumes impact model. The Eulerian dispersed phase (EDP) model was used to simulate the water spray into the exhaust gas. The accuracy and effectiveness of the gas-liquid flow model are verified by a good agreement between simulation results and experimental data. On this basis, a series of numerical simulation studies under different water injection position are performed. The results show that the high temperature regions, along the axis of engines on the deflector plate, have no significant temperature decreasing effect by water spray from the nozzles mounted on the apex of the deflector, and the high temperature converts a large quantity of water into vapor near the plume boundary, which would decrease the flow conductivity. With the cooling spray nozzle fixed directly to the deflector plate, the temperature decrease effect is obvious and the effect of thermal shock on deflector plate induced by exhaust plume is reduced, so that it can prevent the flame deflector from thermal ablation. The study results provide indepth information and engineering guidance for designing the water spray systems and increasing the safety of the launch process.     

Reactive-diffusion waves in the mesospheric photochemical system

The influence of horizontal eddy diffusion on photochemical oscillations of minor gas constituents in the mesopause region of the Earth’s atmosphere is investigated. It is shown that, when the spectrum of oscillations contains a pronounced second subharmonic (nonlinear response of the photochemical system to diurnal variations of solar radiation), reaction-diffusion waves in the form of travelling fronts and pulses of the phase of two-day oscillations may be excited in this region of the atmosphere.     

毛细泵环路系统运行特性的数值研究

给出了描述毛细泵环路(CPL)系统运行特性的非稳态模型,并运用该模型模拟了系统的启动过程,考察了储液罐中温度波动以及蒸发器上热负荷的突然改变对系统稳定性的影响;从数值模拟的角度更好地预测和分析CPL系统运行的过程和特点,该模型的数值结果与实验现象和实验数据相比有较好的一致性。通过该模型还可以进一步揭示CPL系统运行过程中启动困难、储液罐温度不能波动过大以及热流密度突然改变引起系统失效等内在原因,为设计出性能优良的CPL系统提供了理论依据。     

毛细管束中层流粘性振荡流强化传热的若干问题

本文是作者从事振荡管流换热研究的总结。研究结果表明:流体在管内作轴向振荡运动时,可以极大地强化轴向的传热。本文给出了计及管壁效应的振荡管流换热的精确解析解,公布了变Pr数的实验结果。在此基础上,讨论了影响振荡管流轴向换热的6个无因次参数的物理含义,并指出其中的某些无因次参数在物理本质上就是傅里叶数的倒数的平方根,这将有利于理解振荡管流换热这种非定常换热过程。由本文的精确解析解,经过简化,可以得到国内外已公布的近似解。实验数据和解析解预言的基本规律符合很好。