开式转子发动机齿轮传动系统设计技术研究

等速对转行星齿轮传动系统是对转风扇开式转子发动机的关键技术。与齿轮驱动单级风扇(GTF)发动机的行星齿轮传动系统相比较,该系统的结构更为复杂,工作条件更恶劣。本文以对转风扇开式转子发动机齿轮传动系统概念设计为基础,开展了行星齿轮传动系统初步设计、齿轮疲劳强度分析、行星轴承寿命分析和传动系统润滑设计技术研究,为开式转子发动机的发展提供参考。     

Effects of Low Energetic Neutral Atoms on Martian and Venusian Dayside Exospheric Temperature Estimations

The heating of the upper atmospheres and the formation of the ionospheres on Venus and Mars are mainly controlled by the solar X-ray and extreme ultraviolet (EUV) radiation (λ = 0.1–102.7 nm and can be characterized by the 10.7 cm solar radio flux). Previous estimations of the average Martian dayside exospheric temperature inferred from topside plasma scale heights, UV airglow and Lyman-α dayglow observations of up to ∼500 K imply a stronger dependence on solar activity than that found on Venus by the Pioneer Venus Orbiter (PVO) and Magellan spacecraft. However, this dependence appears to be inconsistent with exospheric temperatures (<250 K) inferred from aerobraking maneuvers of recent spacecraft like Mars Pathfinder, Mars Global Surveyor and Mars Odyssey during different solar activity periods and at different orbital locations of the planet. In a similar way, early Lyman-α dayglow and UV airglow observations by Venera 4, Mariner 5 and 10, and Venera 9–12 at Venus also suggested much higher exospheric temperatures of up to 1000 K as compared with the average dayside exospheric temperature of about 270 K inferred from neutral gas mass spectrometry data obtained by PVO. In order to compare Venus and Mars, we estimated the dayside exobase temperature of Venus by using electron density profiles obtained from the PVO radio science experiment during the solar cycle and found the Venusian temperature to vary between 250–300 K, being in reasonable agreement with the exospheric temperatures inferred from Magellan aerobraking data and PVO mass spectrometer measurements. The same method has been applied to Mars by studying the solar cycle variation of the ionospheric peak plasma density observed by Mars Global Surveyor during both solar minimum and maximum conditions, yielding a temperature range between 190–220 K. This result clearly indicates that the average Martian dayside temperature at the exobase does not exceed a value of about 240 K during high solar activity conditions and that the response of the upper atmosphere temperature on Mars to solar activity near the ionization maximum is essentially the same as on Venus. The reason for this discrepancy between exospheric temperature determinations from topside plasma scale heights and electron distributions near the ionospheric maximum seems to lie in the fact that thermal and photochemical equilibrium applies only at altitudes below 170 km, whereas topside scale heights are derived for much higher altitudes where they are modified by transport processes and where local thermodynamic equilibrium (LTE) conditions are violated. Moreover, from simulating the energy density distribution of photochemically produced moderately energetic H, C and O atoms, as well as CO molecules, we argue that exospheric temperatures inferred from Lyman-α dayglow and UV airglow observations result in too high values, because these particles, as well as energetic neutral atoms, transformed from solar wind protons into hydrogen atoms via charge exchange, may contribute to the observed planetary hot neutral gas coronae. Because the low exospheric temperatures inferred from neutral gas mass spectrometer and aerobraking data, as well as from CO⁺ ₂ UV doublet emissions near 180–260 nm obtained from the Mars Express SPICAM UV spectrograph suggest rather low heating efficiencies, some hitherto unidentified additional IR-cooling mechanism in the thermospheres of both Venus and Mars is likely to exist. An erratum to this article can be found at     

模拟月壤可行驶性的离散元数值分析

基于模拟月壤扫描电镜显微照片,建立土颗粒的几何模型,提出不规则形状颗粒群系统的生成策略,构建模拟月壤颗粒间接触的简化本构模型,并利用量纲分析法和双轴压缩试验离散元模拟,建立土宏观力学特性与细观模型参数的关系,结合模拟月壤的三轴压缩试验数据确定离散元模型参数.在月球重力环境下,对轮-土交互作用进行离散元模拟,推导土壤推力的细观表达式,定性分析不同滑转率时土颗粒的动态行为,定量分析模拟月壤的可行驶性.研究结果表明,土壤推力随滑转率的提高而增大;当车轮以高滑转率行驶时,土壤推力相对行驶时间存在瞬态和稳态2个阶段,并且瞬态值高于稳态值.     

公-自转耦合的滚针轴承保持架振动特性

建立了含公-自转耦合的行星轮滚针轴承动力学微分方程组,采用gear stiff（GSTIFF）变步长积分算法对微分方程组进行求解,对比研究了有无公转工况下保持架的打滑率和振动特性,分析了公-自转耦合工况下结构参数和工况参数对两者的影响。结果表明:纯自转工况下保持架振动加速度幅频图各倍频处对应1个幅值,公-自转耦合工况下各倍频处对应2个幅值;在公-自转耦合工况下,保持架振动幅值随径向力和公转速度的增大而增大,随自转速度的增大而减小,存在一个最优间隙比,即间隙比为1左右时使保持架振动幅值最小;保持架打滑率变化趋势与纯自转时一致,但数值减小且减幅越来越大;综上,公-自转耦合工况下会增大保持架径向振动特性,减小周向振动特性。      

内齿轮传动啮合齿面稳态温度场分析

以2K-V行星传动机构中齿轮为研究对象,以齿轮啮合原理、传热学等为理论依据,分析了齿轮在不同啮合位置的相对滑动速度和齿面的接触应力的变化规律。精确计算了稳态温度场边界条件,包括齿轮一个啮合周期内的平均摩擦热流量和不同齿面的对流换热系数。建立单齿三维模型并导入ANSYS Workbench进行温度场的有限元分析。通过将啮合齿面划分成多个沿齿宽方向的条形区域来实现不同啮合位置摩擦热流量的加载,得到齿轮稳态温度场分布,并分析了条形区域的数量对温度场的影响。结果表明,当条形区域数量多于50时,温度场基本趋于稳定。     

行星机构的可靠性分析与计算

行星机构的结构设计缺陷、制造与安装误差、支撑构件刚度不足等原因可能会使系统发生一定程度的偏载,从而会影响整个机构的使用寿命与可靠性。利用最小次序统计量的概念建立了行星齿轮系的可靠度计算模型,模型反映了偏载对齿轮系可靠性的影响。首先,对行星机构进行了详细的运动学和力学分析,计算得到了各个齿轮的随机载荷历程。根据Miner线性疲劳累积损伤法则,将随机载荷历程转化为等效恒幅载荷谱,并将其作为可靠性模型的载荷输入变量。然后,将特定齿轮的疲劳寿命数据进行统计处理,将统计结果作为可靠性模型的强度输入变量。最后,根据模型的计算结果定量地说明了偏载对行星齿轮系可靠性的影响程度,同时利用随机截尾数据处理方法对可靠性模型的有效性进行了验证。     

1-D dusty photo-ionization models of WR planetary nebulae NGC 2452 and IC 2003

We report dusty photo-ionization models for two Planetary Nebulae NGC 2452 and IC 2003, which have [WR] type central stars, using 1D photo-ionization code Cloudy17.02. We used the medium resolution optical spectra and archival IRAS photometry to constrain our models. The physical size of the ionized nebula derived using accurate distance measurements and absolute H$\beta$ flux available in the literature were used as additional constrains. We examine the importance of photo-electric heating and found that models with and without considering photo-electric heating do not make significant difference for both PNe for the MRN grain size distribution considered in this study. We derive the nebular elemental abundances of these PNe by the empirical method as well as by making dusty photo-ionization models. The values of N/O ratios for both PNe obtained from our models are lower than their respective values arrived using empirical methods. The central stars are assumed to be black bodies and the photospheric temperatures derived respectively for NGC 2452 and IC 2003 from their best fit models are 182 kK and 155 kK and their respective luminosities are 630$L_{\odot }$ and 1015$L_{\odot }$. We propose that both the PNe were resulted from low-mass progenitors of mass $?$2.8 M_⊙.