工件淬火过程表面综合换热系数的测算

表面换热系数是温度场计算中一个重要参数,它的取值将直接影响到温度场计算的精度。为了得到表面换热系数与温度变化的关系,采用非线性估算法,编制计算程序,基于工件淬火过程的实测温度值,对工件在不同淬火介质中冷却过程的表面换热系数值随温度的变化进行了测算,得出了换热系数在冷却过程不同阶段的变化规律。     

A Comparative Study of the Influence of the Active Young Sun on the Early Atmospheres of Earth, Venus, and Mars

Because the solar radiation and particle environment plays a major role in all atmospheric processes such as ionization, dissociation, heating of the upper atmospheres, and thermal and non-thermal atmospheric loss processes, the long-time evolution of planetary atmospheres and their water inventories can only be understood within the context of the evolving Sun. We compare the effect of solar induced X-ray and EUV (XUV) heating on the upper atmospheres of Earth, Venus and Mars since the time when the Sun arrived at the Zero-Age-Main-Sequence (ZAMS) about 4.6 Gyr ago. We apply a diffusive-gravitational equilibrium and thermal balance model for studying heating of the early thermospheres by photodissociation and ionization processes, due to exothermic chemical reactions and cooling by IR-radiating molecules like CO₂, NO, OH, etc. Our model simulations result in extended thermospheres for early Earth, Venus and Mars. The exospheric temperatures obtained for all the three planets during this time period lead to diffusion-limited hydrodynamic escape of atomic hydrogen and high Jeans’ escape rates for heavier species like H₂, He, C, N, O, etc. The duration of this blow-off phase for atomic hydrogen depends essentially on the mixing ratios of CO₂, N₂ and H₂O in the atmospheres and could last from ∼100 to several hundred million years. Furthermore, we study the efficiency of various non-thermal atmospheric loss processes on Venus and Mars and investigate the possible protecting effect of the early martian magnetosphere against solar wind induced ion pick up erosion. We find that the early martian magnetic field could decrease the ion-related non-thermal escape rates by a great amount. It is possible that non-magnetized early Mars could have lost its whole atmosphere due to the combined effect of its extended upper atmosphere and a dense solar wind plasma flow of the young Sun during about 200 Myr after the Sun arrived at the ZAMS. Depending on the solar wind parameters, our model simulations for early Venus show that ion pick up by strong solar wind from a non-magnetized planet could erode up to an equivalent amount of ∼250 bar of O⁺ ions during the first several hundred million years. This accumulated loss corresponds to an equivalent mass of ∼1 terrestrial ocean (TO (1 TO ∼1.39×10²⁴ g or expressed as partial pressure, about 265 bar, which corresponds to ∼2900 m average depth)). Finally, we discuss and compare our findings with the results of preceding studies.     

Galactic Wind: Mass Fractionation and Cosmic Ray Acceleration

The dynamical and chemical effects of the Galactic Wind are discussed. This wind is primarily driven by the pressure gradient of the Cosmic Rays. Assuming the latter to be accelerated in the Supernova Remnants of the disk which at the same time produce the Hot Interstellar Medium, it is argued that the gas removed by the wind is enriched in the nucleosynthesis products of Supernova explosions. Therefore the moderate mass loss through this wind should still be able to remove a substantial amount of metals, opening the way for stars to produce more metals than observed in the disk, by e.g. assuming a Salpeter-type stellar initial mass function beyond a few Solar masses. The wind also allows a global, physically appealing interpretation of Cosmic Ray propagation and escape from the Galaxy. In addition the spiral structure of the disk induces periodic pressure waves in the expanding wind that become a sawtooth shock wave train at large distances which can re-accelerate “knee” particles coming from the disk sources. This new Galactic Cosmic Ray component can reach energies of a few×10¹⁸ eV and may contribute to the juncture between the particles of Galactic and extragalactic origin in the observed overall Cosmic Ray spectrum.     

The Origin of Mercury’s Internal Magnetic Field

Mariner 10 measurements proved the existence of a large-scale internal magnetic field on Mercury. The observed field amplitude, however, is too weak to be compatible with typical convective planetary dynamos. The Lorentz force based on an extrapolation of Mariner 10 data to the dynamo region is 10⁻⁴ times smaller than the Coriolis force. This is at odds with the idea that planetary dynamos are thought to work in the so-called magnetostrophic regime, where Coriolis force and Lorentz force should be of comparable magnitude. Recent convective dynamo simulations reviewed here seem to resolve this caveat. We show that the available convective power indeed suffices to drive a magnetostrophic dynamo even when the heat flow though Mercury’s core–mantle boundary is subadiabatic, as suggested by thermal evolution models. Two possible causes are analyzed that could explain why the observations do not reflect a stronger internal field. First, toroidal magnetic fields can be strong but are confined to the conductive core, and second, the observations do not resolve potentially strong small-scale contributions. We review different dynamo simulations that promote either or both effects by (1) strongly driving convection, (2) assuming a particularly small inner core, or (3) assuming a very large inner core. These models still fall somewhat short of explaining the low amplitude of Mariner 10 observations, but the incorporation of an additional effect helps to reach this goal: The subadiabatic heat flow through Mercury’s core–mantle boundary may cause the outer part of the core to be stably stratified, which would largely exclude convective motions in this region. The magnetic field, which is small scale, strong, and very time dependent in the lower convective part of the core, must diffuse through the stagnant layer. Here, the electromagnetic skin effect filters out the more rapidly varying high-order contributions and mainly leaves behind the weaker and slower varying dipole and quadrupole components (Christensen in Nature 444:1056–1058, 2006). Messenger and BepiColombo data will allow us to discriminate between the various models in terms of the magnetic fields spatial structure, its degree of axisymmetry, and its secular variation.     

飞行过载对燃烧室化学反应流场影响

为了研究飞行过载对固体火箭发动机燃烧室化学反应流场影响,以Liang模型模化铝滴燃烧,以有限化学反应速率模型模化湍流燃烧,对过载条件下发动机内流场进行了数值分析,数值结果与试验结果取得了趋势上的一致。研究表明,文中采用的数值计算方法可有效重现发动机热结构故障点;飞行过载改变了流场温度、粒子浓度、化学反应速率等参数分布;过载条件下燃烧室绝热结构表面铝滴积聚及剧烈的化学放热反应是导致其异常烧蚀的原因之一,铝滴局部积聚燃烧会导致温度场畸变;热结构设计必须与流动结构匹配。     

直升机附件舱温度场的数值模拟

为考查某型直升机附件舱的热控制能力,采用有限元软件分析了其在强制冷却和自然冷却情况下的温度场分布.应用非结构化网格和有限体积法进行计算区域和控制方程的离散,采用标准k-ε模型封闭湍流控制方程.针对3种冷却系统设计方案,分析了不同冷却气流进口尺寸、相对位置以及不同附件散热量对附件舱温度分布的影响,计算了自然冷却情况下附件舱密闭时的温度场.计算和试验结果均表明,所采用的冷却方案可以满足附件舱冷却的需要.      

电动汽车牵引用水冷异步电机耦合场分析

基于Ansys多物理场仿真分析平台,对1台车用异步电机进行多物理场耦合分析。仿真电机连续运行在额定工况和峰值工况下的温升和热应力,对电机各部分温度场分布进行深入分析,预测电机峰值工况的最长允许时间。通过热-结构的有限元仿真分析电机内部结构的热应力分布,深入分析转子导条端部与端环焊接位置和机壳与铁心过盈配合面的热应力,校核转子导条端部是否存在开焊的风险,并通过热仿真和应力分析计算机壳与铁心在最高温升工况下不发生滑移或涨开的过盈配合量取值。     

磁场对冷镱原子光钟稳定度影响的仿真分析

在光晶格钟运行时，不停起伏的杂散磁场会引入一阶塞曼频移和二阶塞曼频移，从而影响光晶格钟的频率不稳定度。此外，突变的磁场可能导致激光频率参考到钟跃迁频率的伺服闭环过程发生不可恢复的失锁，从而阻碍光钟的持续运行。在实验中，光钟进行频率闭环锁定前，通常通过控制三维线圈对光钟主腔中心原子处的杂散磁场进行补偿。首先使用三维磁强计，对真空主腔附近的磁场进行监测和记录，以分析杂散磁场对光钟性能的影响。然后利用正态分布模型和二项分布模型等，对光钟频率伺服锁定过程的阿伦偏差进行仿真拟合。在引入实际磁场监测数据的基础上，模拟光钟频率的伺服锁定过程，分析其仿真结果可以得出：减小杂散磁场起伏和控制磁场漂移，在提高冷镱原子光钟的短期稳定性和长期稳定性方面具有重要意义。     

阵列式表面电弧等离子体气动激励控制三角翼流动分离的实验

为探索多路阵列式微秒脉冲表面电弧放电(μs-SAD,Microsecond pulse surface arc discharge)对尖前缘小后掠三角翼流动分离的控制效果和作用机理,首先通过放电测试和纹影测试对多路阵列式μs-SAD的激励特性进行研究,揭示其对流场的作用原理,进一步将多路阵列式μs-SAD用于三角翼流动控制,开展了小后掠三角翼流动分离控制低速风洞实验,研究了来流速度、激励电压和激励频率等参数对控制效果的影响规律。结果表明:多路阵列式μs-SAD能够快速放热,单路瞬间放电能量可达68mJ,在流场局部可诱导产生冲击波;机翼前缘多路阵列式μs-SAD能有效改善三角翼大迎角气动特性,当来流速度为30m/s时,使最大升力系数提高27.2%,失速迎角推迟4°;来流速度增大到40m/s时,流动控制效果减弱,使最大升力系数提高15.5%;存在最佳激励频率使无量纲频率F+=1时,控制效果最好;激励电压存在阈值,其随来流速度的增加而增大,当激励电压超过阈值电压继续增大时,流动控制效果不再增强。     

扫频式射流对涡轮叶栅间隙泄漏流动影响的数值研究

为控制涡轮叶栅中叶顶间隙泄漏流动和改善涡轮气动性能,将扫频式射流器(SJA)作为一种主动流动控制方法应用在涡轮叶栅的研究中。通过非定常数值计算,分析了SJA对涡轮叶栅叶顶间隙流动的作用过程以及作用机理,并且研究了不同工况下SJA对涡轮叶顶流场改善效果以及不同频率的SJA对叶顶流场的影响。结果表明:通过在涡轮叶栅上端壁增加单个SJA装置,可以有效地延迟上端壁的流动分离,其中最佳方案射流流量仅为进口总流量的0.35%,涡轮叶栅出口截面总压损失系数减少了11.48%。存在着最佳的频率284Hz,使SJA装置对流场的作用效果最佳,有效地改善了涡轮叶栅内的间隙流动。