斜爆轰发动机流动机理分析

为了研究高Mach数超燃冲压发动机和斜爆轰发动机的内流场燃烧流动机理，首先用CJ爆轰理论对超燃冲压发动机的内流场特性进行了理论分析，给出了燃烧室流场的气动规律，理论分析结果与现有实验结果吻合得非常好.其次，根据理论分析结果，提出了高Mach数超燃冲压发动机和斜爆轰发动机的气动设计原则.最后，根据提出的气动设计原则，设计了高Mach数斜爆轰发动机，飞行Mach数为9，对斜激波诱导燃烧机理开展了二维数值模拟研究.数值模拟结果表明，在高Mach数下，斜爆轰发动机燃烧室内可以得到稳定的燃烧流场.      

进口条件对超燃冲压发动机氢气燃烧流场特性的影响分析

对不同进口条件下的超燃冲压发动机燃烧室内氢气喷流超声速燃烧流动特性进行了数值模拟与分析.宽范围超燃冲压发动机是吸气式高超声速飞行器推进系统设计中的热点问题之一,受实验设备硬件条件及实验技术限制,数值模拟技术仍然是超燃冲压发动机燃烧室内燃气燃烧特性及流场特性的主要研究手段.采用基于混合网格技术的多组元N-S方程有限体积方法求解器,在不同进口Mach数及压强条件下,对带楔板/凹腔结构的燃烧室模型氢气喷流燃烧流场进行了数值模拟,对比分析了氢气喷流穿透深度、喷口前后回流区结构、掺混效率及燃烧效率等流场结构与典型流场参数的变化特性及影响规律.研究成果可为宽范围超燃冲压发动机喷流燃烧流动特性分析提供参考.      

JF12激波风洞高Mach数超燃冲压发动机实验研究

针对高Mach数（Ma ≥ 7）超燃冲压发动机高气动阻力下的燃烧组织问题,提出一种双突扩燃烧室结构方案.使用数值模拟方法考察了射流与双突扩燃烧室组合方式的混合燃烧特性.设计了双突扩超燃冲压发动机模型,在力学研究所JF12长试验时间激波风洞内,开展了Ma=7.0和Ma=9.5的氢燃料点火和燃烧试验对比.在风洞有效试验时间100 ms内,实现了Ma=7.0和Ma=9.5超燃冲压发动机的成功点火与稳定燃烧.在Ma=7.0情况下,进气道采用三维压缩,燃烧室入口设计Mach数Ma_c=2.5,壁面压力分布实验结果显示燃烧放热靠近燃烧室扩张段上游;在Ma=9.5情况下,进气道采用二维压缩,燃烧室入口设计Mach数Ma_c=3.5,由于燃烧室流动速度特别高,燃烧放热靠近燃烧室扩张段下游.      

采用纹影法的微型航空发动机尾喷温度场测量方法

航空发动机作为飞机上的核心动力装置,对其运行状态的监测,可以提高飞机的安全性与经济性。航空发动机尾喷温度场蕴含着燃烧室内部燃料燃烧程度等有效信息,对其温度场的监测可实现对发动机运行状态的评估。传统的温度场测量方法一般采用单点温度计测量法、激光诱导荧光法(LIF)、可调谐半导体激光法(TDLAS)等,单点温度计测量法测量数据较离散、LIF设备应用复杂、TDLAS仪器设备价格昂贵。因此针对传统测量方法所存在的问题,提出了纹影测量法。首先需要纹影系统对温度场进行纹影成像,得到正确的纹影图像;根据纹影图像求得截面的折射率分布;根据折射率分布算得温度场分布,实现对温度场的测量。纹影测量法是一种非接触、高精度的测量方法,且无需特殊的激光收发装置。实验证明该方法可有效地应用于实验室微型涡喷发动机尾喷区域温度场的测量,可进一步为航空发动机的状态监测提供支持。     

可视化聚焦纹影系统实现流场中的三维扰动成像

可视化成像系统可以实现流场中扰动信息的捕获。针对光学纹影系统,分别从理论和实验上对比研究了流场中的三维超声扰动成像。因三维超声场在光传播方向上引起的流体介质密度变化不同,光波穿过密度变化的流场时,其相位累积变化使图像不能真实反映声场的扰动特征。线型栅的聚焦纹影系统因其线型栅会产生多刀口滤波的作用,故不能对流场中的三维超声扰动场实现完整成像。为了获得流场中的三维扰动特征,提出了采用环型源栅和刀口栅的改进聚焦纹影系统。结果表明:由改进聚焦纹影装置得到的图像扰动特征与实际流场中超声扰动特征相一致;结合图像重构技术,实现了流场中三维复杂扰动的重构。     

超声速预混可燃气流的点火与燃烧

在激波风洞一激波管组合设备上开展了碳氢燃料超声速预混可燃气流的点火与燃烧实验研究。实验结果表明:利用激波对燃料进行预热,并以高温燃气作为引导火焰,可以有效缩短汽油空气超声速可燃混气的点火延迟时间,使之缩短到 0.2 ms以下。利用纹影照片对超声速燃烧流场结构作出了分析;研究了超声速预混可燃气流的温度以及当量比对超声速燃烧流场结构、点火与火焰传播特性的影响。     

燃烧场参数的激光诊断技术研究

 介绍了燃烧场参数的激光诊断技术的研究进展，给出了用自发拉曼散射、激光诱导荧光、相干反斯托克斯拉曼散射法诊断燃烧场温度和组分的实验系统和部分实验结果，单次测量火焰的温度和组分浓度相对误差小于10%；利用平面激光诱导荧光技术获得了稳定燃烧场二维OH荧光图像，并分析了激光作用区域火焰二维温度场的分布。     

基于BOS的超声速流场瞬态密度场的可视化

瞬态密度场的可视化对于超声速流场复杂流动机理研究有着重要的参考价值.设计了基于脉冲激光照明的瞬态密度场可视化系统,针对非对称尖锥模型在Ф=120 mm激波风洞开展了双方向密度场可视化应用研究,获得了Ma=6条件下激波流场清晰的瞬态和长曝光背景纹影图像.研究表明,瞬态背景纹影图像曝光时间为10 ns,能够有效"冻结"超声速流场;相对于长曝光纹影图像,瞬态图像显示了更小时间尺度的流场密度场,且突起较多,分布不均匀.结果表明,瞬态密度场可视化技术能够揭示瞬态激波流场的密度场细节,为超声速和高超声速流场复杂流动机理的深入理解和研究提供了一种有效方法.      

弹头激波诱导燃烧特性的数值模拟

为了研究弹头激波诱导燃烧，基于有限体积的考虑化学反应的Navier-Stokes（N-S）方程，对预混氢气-空气化学恰当比时的燃烧流场进行了数值模拟.时间项基于2阶隐式LU-SGS格式，对流项基于Steger-Warming进行离散，化学反应源项采用对角化隐式处理.首先，研究了网格对燃烧爆轰流场结构的影响，并利用Lehr实验结果验证了计算方法的可靠性；其次，研究了弹头的飞行Mach数（Ma=4.18，5.11，6.46）、弹头直径（D=5，10，15 mm）对燃烧流场稳定性的影响.研究表明:计算网格对氢气-空气爆轰流场结构影响很大；弹头直径一定时，氢气-空气燃烧流场稳定性随着飞行Mach数的增大而增强；弹头飞行Mach数一定时，氢气-空气燃烧流场稳定性随着弹头直径减小而增强.      

带喷流超声速后台阶流场精细结构及其运动特性研究

采用基于纳米示踪的平面激光散射技术(NPLS)对带超声速喷流的后台阶流动精细结构进行了研究. 来流马赫数为3.4, 喷流实测马赫数为2.45, 而名义马赫数为2.5. 结果清晰地揭示了激波、剪切层、混合层、Kelvin-Helmholtz涡、羊角涡及湍流大尺度结构等大量典型流场结构. 基于大量流场精细结构图像, 对典型位置处的结构进行了空间两点相关性分析, 在喷流混合层前端涡结构小于湍流充分发展的尾端, 结构角相对也小. 喷流工作时, 模型台阶下游表面由一薄层气膜覆盖. 获得了模型流向和不同高度展向平面内的流场结构, 对照纹影试验结果, 分析了流动特点及时间演化规律. 采用微型压力扫描系统测试了模型表面的压力系数分布, 靠近喷流下游处压力系数区域0.0146. 针对NPLS图像做了流动的分形维数的分析, 发现在流动初始阶段分形维数接近于1, 越靠下游分形维数越高.     

Supercontinuum laser illumination applied to traditional optical flow imaging methods

The schlieren method of refractive flow visualization traditionally requires non-coherent illumination in order to avoid problems with coherent artifact noise and binary cutoff by the knife-edge. Related shadowgraph and Wollaston-prism schlieren-interferometer methods, however, work well with light sources of high spatial coherence. Here we apply a supercontinuum laser as a light source for these methods, providing spatially coherent white-light illumination. Excellent results are obtained with shadowgraphy and schlieren-interferometry, but the schlieren method still requires a modified cutoff in place of the traditional knife-edge for laser illumination. Once they become widely available, supercontinuum lasers will find frequent use in these optical instruments, especially the schlieren-interferometer.     

Effect of Airy disk on schlieren diffraction interferometer

Schlieren is among the oldest and widely used optical techniques for detection of change in refractive index in transparent media. Present work demonstrates the effect of the position of schlieren element in the Airy pattern on the schlieren interferogram. It has been shown that the amplitude of the diffracted wave, starting from schlieren element and serving as an inbuilt reference beam for the schlieren diffraction interferometer, becomes maximum when schlieren element diffracts light from the Airy disk. Effect of F-number of the optical system on schlieren pattern is also demonstrated via observations on the amplitude of diffracted light.     

Schlieren “PIV” for turbulent flows

The possibility of using commercial PIV equipment combined with schlieren optics to measure the velocity fields of turbulent flows is explored. Given a sufficiently high Reynolds number and adequate refractive flow differences, turbulent eddies can serve as the PIV “particles” in a schlieren image or shadowgram. The PIV software analyzes motion between consecutive schlieren or shadowgraph frames to obtain velocity fields. Velocimetry examples of an axisymmetric sonic helium jet in air and a 2D turbulent boundary layer at Mach 3 are shown. Due to optical path integration, axisymmetric flows require the inverse Abel transform to extract center-plane velocity data. Conditions for optimum schlieren sensitivity are examined. In its present embodiment, “schlieren PIV” is not useful for laminar flows nor for fully 3D flows. Otherwise it functions much like standard PIV under conditions where individual particles are not resolved and velocimetry is instead based on correlation of the motion of turbulent structures. “Schlieren PIV” shows significant promise for general refractive turbulent flow velocimetry if its integrative nature can be overcome through sharp-focusing optics.     

Schlieren成像和声场可视化

Schlieren技术是利用声场引起透明媒质光折射率的变化而实现声场可视化的光学成像技术。它具有对声场无干扰、快速、瞬态成像的特点。本文利用二维光学Fourier变换分析了Schlieren技术的成像原理,在采用连续激光和高速ICCD的Schlieren成像系统中,实验研究了平面波声场和线聚焦声场中换能器光学校准方法和声压的定量检测技术。发展声场瞬态和动态成像技术,观测了声波的聚焦过程和固-液界面的声场分布和变化。这些结果表明Schlieren技术是一种有效的声场可视化和定量检测的光学成像技术。     

An experimental study of aero-optical aberration and dithering of supersonic mixing layer via BOS

The optical performance of supersonic mixing layer is heavily deteriorated by the aero-optical aberration and dithering of coherent structures, but current measuring methods limit the spatiotemporal resolution in relevant studies. A high resolution whole-field aero-optical aberration and dithering measuring method based on the Background Orient Schlieren (BOS) technique was studied. The systematic structure, sensitivity and resolution of BOS are analyzed in this paper. The aero-optical aberration and dither...     

A Refractive INdex Gradient (RING) diagnostic for transientdischarges or expansions of vapor or plasmas

The refractive index gradient (RING) diagnostic described uses a fast, silicon, photodiode quadrant detector with a differential amplifier to temporally detect the refraction of a CW laser by transient discharges or expansions of vapor, gas, or plasma. The method is a local one-dimensional time-resolved, quantitative, species-discriminating (i.e., atoms or electrons) Schlieren technique. The diagnostic is easy to field, sensitive (the minimum deflection angles detectable are ≈0.3 μrad), and fast (risetime=11±1 ns). Circuit design, performance, and diagnostic theory are discussed. To illustrate the utility of this technique, examples of measurements on LEVIS (laser evaporation ion source), a laser-produced, active, lithium ion source, are given. Measured properties include vapor/plasma production thresholds, expansion velocities, and time-resolved gradient and density spatial profiles. Comparisons of the RING results with measurements using a Faraday cup and a double-floating Langmuir probe are presented     

休伦法在观测溶液浓度分布中的应用

休伦法 (Schlierenmethod)在观察物质流的折射率梯度方面的应用已有相当长的历史。对该方法进行改进 ,将其引入晶体生长的监控领域。介绍了该方法的原理及测量公式 ,并进行了实验观察 ,取得了比较理想的定性结果。结果表明 ,用这一方法可以很方便地观测透明物质或溶液中的折射率梯度或浓度的分布情况 ,特别是在晶体生长检测领域中有着广泛的应用前景。     

Flow visualization and pressure measurement in micronozzles

Micro devices have been widely used in aerospace engineering for years. Engineers are interested in applications of micro devices such as microjets, micro actuators, and micronozzles. The small size nozzles can be used for attitude adjustment and propulsion of micro-satellites or mini-spacecraft. In this paper, convergent-divergent micronozzles have been investigated at supersonic speed with various total pressures and Reynolds numbers. The throat of the micronozzle is 250 micron wide and the nozzle is designed as de Laval type. For the measurements, the Reynolds number at the throat varies from 1200 to 11000 and total pressure varies from 6 psia to 55 psia. Experimental results are obtained with pressure-sensitive paint for pressure measurement and schlieren imaging for flow visualization. Flow visualization is a challenge for conventional techniques due to the small length scales and small depth of the density gradient. A modified schlieren technique is used to increase the sensitivity by taking the ratio of wind-on and wind-off images. Pressure-sensitive paint is also used to obtain global pressure measurement of the flow field and to compare with the schlieren results.