泡沫金属的制备方法及应用

介绍了多孔泡沫金属材料常用的传统制备方法(铸造法、发泡法、烧结法和沉积法)及具体应用。并提出了一种新型的泡沫金属制备方法——喷射电沉积法。     

考虑导热对流和辐射作用的轴对称收扩喷管壁温计算

基于N-S方程求解了包括引射流、加力燃烧室在内的轴对称收扩喷管内外流一体化的流场,建立了考虑导热、对流换热和辐射换热作用的轴对称收扩喷管各层壁温分布的计算模型,包括隔热屏、喷管简体、外调节片三层结构.对某航空发动机进行了多工况计算,燃气的物性随压力、温度和油气比的变化采用了一系列精度较高的计算公式和计算方法.计算结果表明:基于密度求解器求解包含引射流在内的轴对称收扩喷管内外流一体化的跨声速流场是成功的.隔热屏和收扩喷管筒体沿流向温度逐渐升高,喷管筒体壁温在喉部达到最大,在扩张段逐渐降低;收扩喷管外调节片壁温与收扩喷管简体的壁温变化规律相同,但是壁温最大值则位于喉部前某一位置.计算结果与经过试验验证程序的结果符合良好.      

俯仰振荡翼型推阻力转变滞后机制数值研究

扑翼产生的反卡门涡街被认为是一种推力型尾迹,但已有研究指出,随着斯特劳哈尔数(St)增大,低雷诺数下俯仰振荡翼型的净推力产生明显滞后于反卡门涡街的出现。为探究该现象背后的物理机制,对NACA0012翼型在雷诺数1 000条件下作简谐俯仰运动的流场进行了数值模拟。采用翼型表面积分方法和基于有限控制体的气动力估计方法分别研究了翼面分布力特性和尾迹流场特性变化对阻力-推力转变临界点的影响。翼面分布力积分结果表明,当翼型振荡参数进入对应反卡门涡街尾迹形态区域时,翼面压力分布产生的推力分量无法克服剪切层的黏滞阻力,是造成俯仰翼型推力产生滞后于反卡门涡街出现的主要原因。对尾迹流场及相应的推阻力特性变化的分析表明,尽管反卡门涡街会产生"喷流效应",但在St较小时,其产生的动量诱导推力无法克服反卡门涡自身的涡致阻力和尾迹流场压力损失引入的附加阻力,因此即使存在反卡门涡街也不能产生净推力,进而从流场分析的角度进一步解释了这一滞后现象的发生机制。     

Experimental of combustion instability in NTO/MMH impinging combustion chambers

This paper presents an experimental study into dynamics of chamber pressure and heat release rate during self-excited spinning and standing azimuthal mode in NTO/MMH (nitrogen tetroxide/monomethylhydrazine) impinging combustion chambers. Nine cases including two combustion chamber configurations were conducted. The operating conditions of all unstable cases were located in the instability region according to Hewitt empirical correlation. The results show that chamber pressure oscillations keep pace with the corresponding OH* chemiluminescence intensity over the whole combustion region in the spinning and standing modes. It is indicated that the Rayleigh index is positive over the whole combustion area in all the unstable cases. A significant supersonic flame front structure of the first-order spinning mode was found in a cylindrical chamber, which means that a detonation wave could exist in the cylindrical chamber without a center body. The pressure and heat release rate oscillations at the pressure node are nonnegligible although their amplitudes are lower than those at the pressure antinode in the first-order standing mode with an annular chamber. Besides, the dominant frequency of pressure and heat release rate oscillations at the pressure node is twice as high as that at the pressure antinode.     

单股自由圆射流撞壁雾化实验

利用直流撞击式喷注器组织燃烧的发动机推力室喉部材料耐温极限制约了发动机燃烧效率提升,一种新型高性能直流冷壁式喷注器可以解决这一问题,为了指导这种新型喷注器的设计,从射流撞击雾化实验出发,探索了圆射流撞壁雾化规律。采用高速摄影捕获溅射雾化场整体形态,利用收集法测量溅射雾化率,选用PDA和PIV分别测量溅射液滴粒径及速度矢量。研究结果表明:射流撞壁后存在溅射,溅射液滴局部呈现螺旋状,液滴粒径为几十微米量级,溅射雾化率随撞击距离的变化规律可分为4个典型阶段:初始段、发展段、稳定段、衰减段,湍流动能为溅射雾化率的决定因素。     

A model-scale test on noise from single-stream nozzle exhaust geometries in static conditions

A model-scale test with single-stream nozzle exhaust geometries was carried out at the anechoic chamber of Beihang University in Beijing, China. The spectral characteristics are investigated, and the effects of the following parametric variations are reported in this paper: impact of nozzle operating conditions on spectra; impact of the presence of a plug; and effectiveness of chevron configurations for noise mitigation. The measurement shows that the change of pressure values has more impact on spectra than the change of temperature values. The spectral change due to pressure is shown at all band numbers for unheated conditions whereas it is more pronounced at high-frequency ranges for heated conditions. An impact of the presence of a plug is also clearly observed. The reduction of noise is moderate up to band number of 35, and becomes more significant at higher band numbers. It is observed that chevron nozzles are more efficient at high pressure and temperature values. It is expected that the quantified analysis will be used to develop an empirical model of single jet noise, which will be the baseline for the development of prediction of noise from turbofan engines of high bypass ratios.     

超音速流动中侧向喷流干扰特性的数值模拟

通过与实验结果的比较验证Fluent软件可以用于超音速流动中侧向喷流干扰特性数值研究.使用Fluent软件对超音速流动中不同喷流压力和攻角下侧向喷流干扰特性进行的数值研究表明,超音速流动中,随喷流压力和负攻角增大,喷流前的高压区明显增大,喷流的控制效果更好.喷流包裹作用的影响范围在90°弹面内.喷流压力增大,喷流包裹作用加强,影响范围增大.     

设备构件对射流开孔性能的影响

通过对设备构件的结构布局和射流毁伤特性的详细分析,得到2种设备构件的模拟结构,并开展了对射流开孔性能影响的试验。试验结果表明,采用均匀平板模拟的方式能够较准确地模拟设备构件对射流的影响。研究结果对破甲弹的设计具有较好的参考意义。     

基于燃气射流冷凝的氧路系统频率特性研究

基于热力学不平衡两流体六方程模型模拟了液氧煤油补燃循环发动机燃气射流在氧路系统泵间管路液氧流体中的冷凝过程，获得了燃气射流冷凝特征参数沿管路流向的分布规律。根据Rayleigh-Plesset方程和燃气射流特性建立了泵间管路燃气冷凝过程的传递函数模型，并与氧路管路、泵等组件模型联立求解，分析了发动机氧路系统频率特性。研究了在不同氧路入口压力和液氧温度边界条件下，泵间管路燃气射流冷凝过程对氧路系统频率特性的影响，仿真结果表明高入口压力和过冷液氧改变了射流气体的惯性和柔度，使得氧路系统特征频率增大。不同边界条件下发动机热试车结果表明，提高氧路入口压力或降低液氧温度使得氧路系统频率从8.3 Hz提高至11 Hz，与数值仿真结果一致，验证了泵间管燃气射流冷凝过程是影响氧路系统频率特性的重要环节。     

航空发动机整体叶盘磨料水射流开坯加工技术研究进展

整体叶盘结构是航空发动机技术发展的一个重要方向，且多采用难加工材料，如何实现整体叶盘高质高效加工是机械制造领域亟待解决的难题之一。通过高压磨料水射流（AWJ）加工技术实现整体叶盘毛坯的开坯粗加工，是一种有效缩短整体叶盘加工周期、降低昂贵铣削刀具成本、提高开坯效率的工艺手段。本文就磨料水射流加工材料去除机理、复杂曲面轨迹优化、多物理量和机械量参数组合优化和整体叶盘开坯设备概述了国内外的研究现状，在此基础上，针对当前具有复杂曲面结构的整体叶盘开坯面临的关键问题，提出了若干解决思路和技术途径，指出了高压磨料水射流在复杂曲面零件高效加工中的发展趋势。