发动机进气动态畸变测量系统与数据处理

本文介绍了动态畸变测量系统及其数据处理方法.进一步提高采样频率后可将该系统用于飞机和发动机的研究中.     

紊流发生器特性和流场的模拟调节

本文探讨了轴对称紊流发生器总压畸变流场的不稳定性,根据流场低压区的时钟位置和大小是否随时间而变化,可分为稳定型和非稳定型两种.对于稳定场,畸变指数测量的重复性较好,非稳定场则较差.文中还介绍了一种简单而有效的流场模拟调节方法.     

粘性跨音速喷管流场计算

本文继用隐式近似因子分解法成功地计算无粘跨音速喷管流场之后,用同样的方法,结合任意曲线坐标系,通过非定常方程在相当长时间后的定常解,针对矩形截面喷管和轴对称喷管粘性跨音速流场,求解了可压缩层流薄层N-S方程,获得了核心流,特别是边界层中的流动参数.对于矩形截面和轴对称两种喷管进行了计算,其结果和实验数据相当一致.将本文的方法应用到粘性两相流动计算,可望较多的节省机时.     

Semi-analytic Solution of Steady Temperature Fields During Thin Plate Welding

Usually, it is very difficult to find out an analytical solution to thermal conduction problems during high temperature welding. Therefore, as an important numerical approach, the method of lines （MOLs） is introduced to solve the temperature field characterized by high gradients. The basic idea of the method is to semi-discretize the governing equation of the problem into a system of ordinary differential equations （ODEs） defined on discrete lines by means of the finite difference method, by which the thermal boundary condition with high gradients are directly embodied in formulation. Thus the temperature field can be obtained by solving the ODEs. As a numerical example, the variation of an axisymmetrical temperature field along the plate thickness can be obtained.     

CVI反应器内部气体流场的有限元模拟及优化设计

采用有限元计算方法,研究了CVI反应器内部的流场特征.对于形状简单的构件,构件的放置方式和阵列对气体的流动状态具有显著的影响.与横向阵列相比,纵向阵列能充分保证构件沿其长度方向流场均匀性,减小回流现象;在反应器中,随着纵向阵列试样数量的增加和分布均匀性的提高,气体流动速度增大,流场均匀性提高.减少反应器内部的自由空间,是提高流场品质和化学气相沉积效果的关键.基于减少反应器内部的自由空间的原则,针对杯形复杂构件,提出了通过加入与其几何形状相适应的导流板工装,有效避免了在构件内部和外部形成回流区,实现流场的优化设计.     

激光冲击残余应力场的有限元分析

建立模拟激光冲击残余应力场的非线性弹塑性有限元模型,预测AISI 304奥氏体不锈钢厚、薄靶材经激光冲击后表面以及内部的残余应力场分布.模拟过程中,考虑材料高应变率(106s-1)下的力学性能和激光诱导冲击波的精确加载,分析激光功率密度、激光光斑尺寸、激光脉宽、激光冲击次数、激光单面与双面冲击等激光冲击参数以及初始残余应力等因素对不锈钢靶材残余应力分布的影响.数值模拟结果与X射线衍射法测量值吻合较好.在有初始残余拉应力(250MPa)存在的情况下,激光冲击仍能使304奥氏体不锈钢靶材形成残余压应力层,说明激光冲击工艺可提高奥氏体不锈钢焊接构件的抗应力腐蚀开裂能力.     

冷却剂不同流动方式对膨胀循环推力室再生冷却换热的影响

为了解液体火箭发动机膨胀循环推力室再生冷却换热特性,对某一参考发动机推力室和另外两种面积比的膨胀循环推力室建立三维计算模型,采用数值模拟的方法,考察冷却剂的温升、冷却通道压降以及推力室内壁面温度和热流密度的分布情况.重点比较了不同燃烧室圆柱段长度、冷却剂不同流动方式以及不同面积比对以上结果的影响.计算过程中采用二阶迎风格式离散控制方程.计算结果表明:采用逆流冷却时,通过加长推力室圆柱段长度使推力室受热面积增加70%后,冷却剂温升提高了一倍左右;对膨胀循环推力室进行再生冷却时,采用顺流冷却要比逆流冷却的冷却通道压降低,但同时冷却剂温升也较低,并且对喉部壁面的冷却效果较差.     

基于模拟退火算法与响应面模型的三维气动优化设计方法

提出了一套适用于高耗时三维气动设计问题的优化设计体系.其主要思想是采用改进拉丁超立方体试验设计选取样本点,应用自行开发的三维粘性流场求解程序进行流场计算建立数据库,采用二次响应面方法建立近似模型,再应用高效模拟退火算法进行全局寻优.以NASA rotor57为对象,在详细进行流场计算基础上采用所提出的优化体系对其进行了三维积叠优化设计.在对流量、效率加以严格约束的条件下,总压比可提高1.8%,对流场结构进行了分析.优化结果表明本优化方法省时,适于三维气动设计的特点.     

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.