二次流喷射角度对无阻流板式反推装置的影响

对一无阻流门叶栅式反推装置的流场进行了数值与实验研究,详细分析了不同二次流喷射角度对反推性能参数的影响。结果表明二次流喷射喷射角度影响进入反推窗口的气流方向和气流质量,会对反推性能产生影响。存在一个最佳的二次流喷射角度,能使得反推效果最好。当射流顺着风扇气流的偏转方向进行喷射时会产生最大的射入深度,进而使得更多的风扇气流通过反推窗口偏转出去,表现出最优的反推力性能。     

低空大展弦比无人机翼梢磁梯度测量探头气动特性及影响

针对一种低空大展弦比无人机, 文章进行全机和翼梢磁梯度测量探头数值模拟.全机计算给出翼梢磁梯度测量探头对全机气动特性和操稳特性的影响; 翼梢磁梯度测量探头计算实现了气动外形优化设计, 在保持全机操稳特性的前提下, 最大程度地减小全机气动阻力增量.结果表明, 磁梯度测量探头对全机气动阻力增量在9%之内, 俯仰力矩变化在5%之内, 对全机操稳特性的影响不大, 气动外形优化设计基本满足该低空大展弦比无人机的安全飞行技术要求.      

基于物理机制模型的民机机体噪声预测

为实现民机总体方案快速评估与优化迭代设计,文章对民机增升装置前缘缝翼及后缘襟翼分别建立了基于民机噪声物理机制的预测模型,在此基础上搭建了机体噪声预测体系,开发了相应的预测工具UNICRAFT.为评估预测工具UNICRAFT的计算精度和效率,文章分别针对翼吊式布局,前缘缝翼/Fowler式襟翼形式,以及尾吊式布局,前缘缝翼\双缝子翼加后退式襟翼形式的增升装置进行了计算校核验证,通过与声学风洞试验结果对比分析,验证了本文发展的预测工具及预测体系的有效性,能够实现飞机级噪声水平的高效预测.      

杨氏双缝干涉实验与飞机安全着陆系统

杨氏双缝干涉实验是第一个证实光的波动性的著名实验,利用它可测量光的波长,在波动光学的发展中起着重要的作用.在通信领域中,杨氏双缝干涉实验原理构成了飞机安全着陆导航系统的理论基础之一,尤其是能见度不高的天气情况下,尽管实际的安全着陆系统比本文描述的复杂得多,但它们基于相同的原理.本文通过对美国大学物理教材中一道波动光学习题的赏析,简述杨氏双缝干涉实验原理在飞机安全着陆系统中的应用.     

大型民机试飞测试发展与挑战

飞行试验是对飞机的性能进行验证和确认的关键阶段,试飞测试是保障该阶段工作的重要内容;国内目前对于军机已拥有了成熟的测试技术、测试方法和可靠的测试设备,而对于民用飞机特别是大型民机的试飞测试目前还处在起步阶段;随着国家大飞机研制专项的不断推近,大型客机试飞测试需求逐步明确;从大型民机试飞测试需求和测试工作特点出发,对机载测试技术变革、遥测和数据处理技术等键技术在国外的最新发展和国内大型飞机的现状进行对比分析,可以看出我国民机试飞测试在网络化机载测试系统应用、遥测传输链路带宽、大数据快速处理等方面存在较大的挑战;在此基础上对应对挑战的发展策略和后续攻关的方向进行研究,可以为我国大型飞机特别是民机试飞测试技术的发展提供参考。      

飞机激光雷达散射截面测量与分析

飞机激光雷达散射截面的测量,对于研究飞机激光散射特性以及评估探测系统至关重要.本文介绍了飞机激光雷达散射截面测量理论,设计了飞机激光雷达散射截面测量装置和测量方法,并通过实验验证了该装置与测量方法.在全尺寸真实飞机试验与测量过程中,通过对原始数据高斯补偿与背景修正,获得了误差小于7%的飞机激光雷达散射截面数据.实验结果表明,本文提出的飞机激光雷达散射截面测量与分析方法是正确的和有效的.     

欧洲欲制造可从跑道起飞的太空飞机

一个欧洲研究小组正在开发新一代Skylon太空飞机．这种太空飞机可重复使用,能将超过12t的货物送入轨道,起飞和着陆使用的跑道相同,并有望在lO年内问世．飞机研制的成败取决于“佩刀”（Sabre）火箭发动机．“佩刀”是一种独特的混合动力发动机,在地球大气层中,能像传统喷气发动机一样“呼吸”空气;在太空则转换为火箭动力．在吸气模式下,空气先是被冷却并压缩,然后同氢燃料一起进入火箭发动机;在火箭模式下,     

二维传声器阵列测量技术及其对飞机进场着陆过程噪声的实验研究

发展了一种由１１１个传声器组成的Ｍ维平面传声器阵列测量技术,１１１个传声器在平面阵列中的位置应用随机优化的方法确定,从而保证平面传声器阵列在感兴趣的测量频率范围内具有理想的性能,并应用数值模拟的方法检验了平面传声器阵列的频谱特性．应用此平面传声器阵列对当前流行的民用客机进场着陆过程中飞机噪声源进行了测量分析,实验结果表明应用此项技术可以辨别出在飞机表面上所有重要的噪声源,并可获得全尺寸飞机机体重要噪声源的详细的频谱特性、指向特性和声级变化．     

现代涡轮喷气发动机的物理原理

国产C919大飞机实现了中国人的大飞机梦,发动机是大飞机的心脏.以涡轮喷气发动机的产生和发展为载体,在与活塞发动机比较的基础上,分析涡轮喷气发动机的物理原理,探讨了不同类型的发动机对飞机飞行效率的影响,可以增加中学生“物理·技术·社会”的认识.     

LNG装置部分负荷下动态特性的仿真研究

天然气MRC液化装置的动态运行特性对其设计和操作运行有指导意义.MRC系统的动态特性主要取决于循环工况和离心机组运行工况的匹配.采用HYSYS软件建立了液化工艺模型,采用相似准则和工作特性曲线对离心机组的运行工况进行模拟计算.其中特性曲线采用描点并插值查表法进行计算.对部分负荷下液化单元的动态特性进行了仿真研究.在同样...     

Assessment of community noise for a medium-range airplane with open-rotor engines

Community noise of a hypothetical medium-range airplane equipped with open-rotor engines is assessed by numerical modeling of the aeroacoustic characteristics of an isolated open rotor with the simplest blade geometry. Various open-rotor configurations are considered at constant thrust, and the lowest-noise configuration is selected. A two-engine medium-range airplane at known thrust of bypass turbofan engines at different segments of the takeoff–landing trajectory is considered, after the replacement of those engines by the open-rotor engines. It is established that a medium-range airplane with two open-rotor engines meets the requirements of Chapter 4 of the ICAO standard with a significant margin. It is shown that airframe noise makes a significant contribution to the total noise of an airplane with open-rotor engines at landing.     

湍流模型在复杂流场数值模拟中的应用

采用4种湍流模型:代数Baldwin Lomax(B-L)模型、半方程Johnson King(J-K)模型的两个版本(J-K90A和J K92)以及两方程k-g模型,分别数值模拟了导弹超音速流动、NASATND-712标模和民机翼身组合体(两区C-O网格)跨音速流动.采用中心有限体积和多步Runge-Kutta方法数值积分三维可压缩雷诺平均Navier-Stokes(N-S)方程组.k-g湍流模型方程的求解采用类似于N-S方程组的方法进行.所有湍流模型均能很好地模拟附体及小分离流动;对于大攻角、分离剧烈的导弹流动,k-g和J-K92模型与实验吻合更好;B-L模型在模拟民机跨音速流动时,它所捕捉的激波位置较其余3种模型靠后.利用多块网格模拟民机翼身组合体流场时,k-g模型的模拟能力强于其余3种模型.     

Cabin attendants’ exposure to vibration and shocks during landing

The Scandinavian Airlines System (SAS) has noted that cabin attendants have reported an increase in health problems associated with landing. The European Union reports cover health problems related to neck, shoulder, and lower-back injuries. Moreover, analysis of these reports shows that the problems are often associated with specific airplanes that have a longer tail behind the rear wheels and appear more often in attendants who sit in the back of planes rather then the front. Against this background, this study measures and describes the vibration during landing in specific airplanes to evaluate the health risk for the cabin attendants.Measurements were conducted on regular flights with passengers in the type of airplane, Boeing 737-800, which was related to the highest per cent of reported health problems. All measurements were performed the same day during three landings in one airplane with the same pilots and cabin attendants. The measurements were carried out simultaneously on the cabin crew seats in the back and front of the passenger cabin. Under the cabin crew's seat cushions, a triaxiell seat-accelerometer was placed to measure the vibration in three axes. The signals from the accelerometers were amplified by charge amplifiers and stored on tape. The stored data were analysed with a computer-based analyse system.For the cabin attendants, the dominant direction for the vibration load during landing is the up-and-down direction although some vibration also occurs in the other horizontal directions. The exposure to vibration is higher on the rear crew seat compared to the front seat. For instance, both the vibration dose value (VDV) and the frequency-weighted acceleration in the dominant direction are more then 50% higher on the rear seat. The frequency-weighted acceleration and the VDV measured at the crew seats are below the exposure limits as described by the European vibration directive. The evaluation of the cabin attendants’ exposure to multiple shocks during landing shows that the potential of an adverse health effect for the cabin attendants is low in the front of the airplane and increases to moderate in the rear. Although this is a limited study, it could be conclude that there could be a risk for cabin attendants due to the exposure of multiple shocks. Therefore, efforts should be spent to minimize their risk by developing a better seat cushion and back support to lessen the effects of shocks. In addition, attendants should be informed about the most suitable posture to take during landing.     

半导体带间级联激光器研究进展

半导体带间级联量子阱是实现3~5μm波段中红外激光器的重要前沿,其在半导体光电器件技术、气体检测、医学医疗以及自由空间光通信等诸多领域具有重要科学意义和应用价值。半导体带间级联量子阱发光机理是以二类量子阱中的电子与空穴的带间辐射复合发光为主导,再通过电子注入区与空穴注入区形成级联放大,实现多个量子阱周期内电子与空穴的重复利用。本文综述了半导体带间级联激光器从提出能带结构、外延材料到器件制备技术的发展历程,剖析了器件结构各功能区基本概念和工作原理,介绍了器件结构设计与制备工艺技术难点的里程碑突破,详细解释了载流子再平衡、分别限制层等设计,最后展望了半导体带间级联激光器的发展方向和趋势。     

多功能向心力测量转台

多功能向心力测量转台应用控制变量法,实现对向心力规律的全面定量探究;也可用于"弯道受力分析、滚桶脱水、柱形墙内的水平圆周运动、法拉第电磁感应定律"等典型物理问题的教学.装置采用变频电源驱动同步电动机的方式来实现匀速转动,调速和计速一步到位,无需电磁或光电门测速装置;利用手持电子秤代替弹簧秤或拉力传感器,从而免去了DIS...     

Controllable electromagnetically induced grating in a cascade-type atomic system

A controllable electromagnetically induced grating (EIG) is experimentally realized in a coherent rubidium ensemble with 5S_1/2–5P_3/2–5D_5/2 cascade configuration. In our work, a whole picture describing the relation between the first-order diffraction efficiency and the power of the coupling field is experimentally presented for the first time, which agrees well with the theoretical prediction. More important, by fine tuning the experimental parameters, the first-order diffraction efficiency of as high as 25% can be achieved and a clear three-order diffraction pattern is also observed. Such a controllable periodic structure can provide a powerful tool for studying the control of light dynamics, pave the way for realizing new optical device.     

四程放大系统能流分布的模拟计算和分析

 采用下级能等效寿命来描述多程放大系统的增益恢复问题, 并在此基础上建立了较为准确的多程放大系统能流分布的1维模拟程序。对带小口径电光开关的四程放大系统构型各种基本排布的模拟表明, 采用14张钕玻璃片即能达到单路输出2. 8kJ (1ω, 1.5ns) 的要求。给出了满足要求的排布方案并分析比较了工作特性。     

Use of a plane jet for flow-induced noise reduction of tandem rods

Unsteady wake from upstream components of landing gear impinging on downstream components could be a strong noise source.The use of a plane jet is proposed to reduce this flow-induced noise.Tandem rods with different gap widths were utilized as the test body.Both acoustic and aerodynamic tests were conducted in order to validate this technique.Acoustic test results proved that overall noise emission from tandem rods could be lowered and tonal noise could be removed with use of the plane jet.However,when the plane jet was turned on,in some frequency range it could be the subsequent main contributor instead of tandem rods to total noise emission whilst in some frequency range rods could still be the main contributor.Moreover,aerodynamic tests fundamentally studied explanations for the noise reduction.Specifically,not only impinging speed to rods but speed and turbulence level to the top edge of the rear rod could be diminished by the upstream plane jet.Consequently,the vortex shedding induced by the rear rod was reduced,which was confirmed by the speed,Reynolds stress as well as the velocity fluctuation spectral measured in its wake.This study confirmed the potential use of a plane jet towards landing gear noise reduction.     

襟翼侧缘噪声机理及修型降噪设计

襟翼侧缘噪声是飞机起降阶段机体噪声的重要噪声源。采用极大涡模拟对襟翼侧缘非定常流场进行数值模拟,分析其噪声产生机理.基于此,提出了两种襟翼侧缘修型方式,应用虚拟渗透面的Ffowcs Williams and Hawkings(FW-H)声比拟方法将修型构型的远场噪声频谱特性和指向性与基准构型对比分析,研究其降噪效果。通过流场和声场的数值模拟表明,襟翼侧缘噪声属于宽频噪声。不同的襟翼侧缘形状改变了流场形态、侧缘涡结构以及涡系的发展过程,进而对声源分布和远场噪声特性产生影响。结果表明:在给定的5°计算迎角下,两种襟翼侧缘修型方式在保证增升装置的原有升阻气动特性的前提下,能达到减小全场总声压级1~2 dB的降噪效果。