高动态范围激光焦斑测量数学模型研究

提出了一种高动态范围的激光焦斑测量方法.首先,构建纹影测量远场焦斑数学模型,确定重构需要的参数,并使用准直光路对参数进行标定;其次,运用综合诊断快速自动准直系统使纹影小球遮挡住旁瓣光斑中心,获得准确的旁瓣光斑;最后,改进计算纹影小球中心及图像融合等方面的纹影重构算法,克服了传统纹影重构方法中主瓣旁瓣中心误差大、合并图像拼接边缘台阶明显的缺点.对大型激光装置参数测量综合诊断系统的远场焦斑测量应用表明:通过对纹影测量远场焦斑数学模型中参数的精确标定以及对纹影重构算法的优化,能够实现高动态范围激光焦斑的准确测量.     

激光诱导荧光聚焦纹影系统及超声速燃烧流场应用

纹影是一种常用的流动显示技术,广泛应用于可压缩流动显示及超声速燃烧流场实验.然而,在变Mach数超声速燃烧实验中,燃烧室总温随来流Mach数变化.受准稳态/非定常温度变化影响,光学玻璃窗口的折射率发生显著改变,影响基于密度梯度的纹影成像质量.同时,普通纹影为光程体积沿程积分,难以同二维燃烧场成像信息进行直接比较以开展燃烧与流动耦合研究.聚焦纹影技术可抑制燃烧室内高温引起的玻璃窗口折射率变化,并实现毫米级的急剧聚焦深度,获得二维流场结构,同时配合纳秒级脉宽Nd:YAG激光光源可冻结高超声速流场.在传统聚焦纹影系统基础上发展了激光诱导荧光聚焦纹影系统并应用于变Mach数超声速燃烧实验,创新点在于使用激光诱导荧光染料,以荧光作为光源消除原本激光光源中的相干噪声,同时发展了边缘增强图像处理方法.实验结果表明激光诱导荧光聚焦纹影系统及边缘增强图像处理方法能够有效消除激光光源相干噪声,捕捉二维超声速燃烧流场结构.      

激光烧蚀羽流光学成像效果研究

使用YAG脉冲激光烧蚀固态POM聚合物和掺碳质量分数为5%的液态甘油混合物,形成羽流场.分别在相机镜头前添加滤光片以及在纹影系统中设置不同的刀口,观察对羽流场像的影响.实验结果表明:滤光片和暗场纹影均能够提高羽流纹影图像的显示效果.     

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。     

采用纹影法的微型航空发动机尾喷温度场测量方法北大核心CSCD

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。     

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。     

超高速激光纹影技术测量脉冲功率驱动的磁重联现象

用超高速激光纹影技术测量了Z箍缩等离子体磁重联现象。实验采用超高速光电分幅相机,配合激光纹影技术,测量了XP-1装置上两根金属丝产生的等离子体分布,论证了超高速激光纹影技术研究Z箍缩磁重联现象的可行性。双钨丝实验结果表明,电流加载约10ns后金属丝已有明显膨胀,线性拟合得到平均膨胀速度约8km/s,金属丝内外两侧出现了规则的极有可能是垂直磁场的电热不稳定性扰动,并沿角向高度关联。铝丝负载的实验结果表明,早期的不稳定性波长为0.4mm,电流峰值之后金属丝初始位置仍有大量等离子体,后期的不稳定性波长约1.5mm。这些现象揭示了不稳定性发展的一个主要特征:短波模式受抑制,长波模式将占主导。     

温度场纹影定量测量技术

为了研究纹影系统的温度场定量测量技术,本文详细阐述了纹影技术的定量测量原理,并通过分析流场纹影图像灰度大小与未被遮挡的光源像面积的关系,提出了一种新颖的流场温度定量测量的计算方法。首先,在光学平台上搭建了透射式纹影系统,将加热平台放置在该系统的测量区域,利用CCD相机将采集到的纹影图像上传到上位机进行图像处理,然后采用该算法计算得到温度场的测量值,并与热电偶的测量值相对比。实验结果表明：在室温20℃时,将加热平台的温度分别设定为50℃和90℃,纹影系统测量得到的温度值相对误差小于10%,证明了该计算方法的可靠性,实现了以纹影技术为基础的温度场定量测量。     

激光弹道列阵高速技术的研究

本文简要报导了激光弹道列阵高速摄影的最新研究进展。并对几种方法获得的飞行弹体照片进行了分析比较。 激光光源配合阴影或纹影光学系统。采用适当的同步触发装置。在超高速弹道靶真空靶道上,拍摄了速度为2公里/秒到4.5公里/秒的高速飞行弹体阴影和纹影照片。多台联动也获得了成功     

纹影技术在直喷式柴油机燃烧过程研究中的应用

本文叙述了作者所设计建立的高速纹影摄影光路系统,给出了利用该系统所拍摄的纹影照片,并通过照片简单分析了柴油机缸内的喷雾和燃烧过程。结果表明,纹影技术是研究发动机缸内空气运动和喷雾燃烧过程的有效手段。     

Mathematical Formalism of Nonequilibrium Thermodynamics for Nonlinear Chemical Reaction Systems with General Rate Law

This paper studies a mathematical formalism of nonequilibrium thermodynamics for chemical reaction models with N species, M reactions, and general rate law. We establish a mathematical basis for J. W. Gibbs’ macroscopic chemical thermodynamics under G. N. Lewis’ kinetic law of entire equilibrium (detailed balance in nonlinear chemical kinetics). In doing so, the equilibrium thermodynamics is then naturally generalized to nonequilibrium settings without detailed balance. The kinetic models are represented by a Markovian jumping process. A generalized macroscopic chemical free energy function and its associated balance equation with nonnegative source and sink are the major discoveries. The proof is based on the large deviation principle of this type of Markov processes. A general fluctuation dissipation theorem for stochastic reaction kinetics is also proved. The mathematical theory illustrates how a novel macroscopic dynamic law can emerges from the mesoscopic kinetics in a multi-scale system.     

化学反应与饱和模型对化学氧碘激光性能的影响

 将速率方程（RE）模型与化学动力学模型相结合，讨论了增益饱和模型与化学反应系统对COIL性能的影响。流动为预混的一维模型，考虑了10种成分和21个化学反应，分析计算了未分解碘分子，激发态氧产率，水含量以及温度等因素对COIL性能的影响。计算结果表明，碘流量过多，混合和反应过程中消耗大量能量；碘流量过低，导致粒子数反转和增益过低，对于能量的提取不利。     

Reduced modeling of the NOx formation based on the reaction-diffusion manifolds method for counterflow diffusion flames

The accurate prediction of the NOx formation has gained great attention in view of clean combustion. In this direction, a reliable reduction technique for the chemical kinetics is important to capture the NOx formation accurately with reduced computational costs for the practical turbulent combustion processes. This work focuses on the hierarchical construction of Reaction-Diffusion Manifolds (REDIM) to include the NOx chemistry, which is well-known to be governed by very slow chemical reactions. Based on the hierarchical structure of the REDIM method, a two-dimensional (2D) and a three-dimensional (3D) REDIM model are generated, without any principle extension of the REDIM method. Sample calculations of NOx formation in methane/air non-premixed counterflow flames verify the REDIM method for both steady and transient processes.     

Monitoring chemical and physical changes on sub-nanogram quantities of platinum dioxide

We have measured in real-time the chemical reaction-induced weight loss and variation in physical and mechanical properties of sub-nanogram quantities of deposits utilizing the resonance response of microcantilevers. The hydrogen reduction of sub-nanogram quantities of alpha platinum oxide deposited on micromachined silicon cantilevers and resultant weight loss, as well as the kinetics of this process, were investigated. Comparison with theory suggests that this technique could be a powerful tool to measure physical and chemical changes occurring on sub-nanogram deposits.     

Numerical analysis of chemical reaction processes in different anode attachments of a high-intensity argon arc

The attachment mode of arc on anode is closely related to the non-equilibrium chemical kinetics process of the anode region of arc. In this paper, the detailed chemical reaction mechanisms in the flow-affected region for both diffuse and constricted argon arc attachments are investigated by means of one-dimensional discharge coupled with a single-fluid, two-temperature model. The collisional-radiative model is used to examine the chemical reaction processes occurring in the anode region, including the arc centreline and fringe region. The numerical results are validated by comparison with available experimental data. The obtained radial distributions of electron temperature, electron density, excited states densities, ionization, and recombination processes reveal that different mechanisms dominate the diffuse and constricted arc-anode attachments.     

The mathematical background of chemical reactor analysis: I. Preliminaries. Batch reactors

The name “chemical reaction engineering” has been given to the branch of chemical engineering that focusses on the conditions which make for useful chemical transformation. Within this subdiscipline there are studies related primarily to the static and dynamic behavior of the reactor and of these the more analytical are rich in mathematical problems. In this paper the preliminary considerations of stoicheiometry, thermodynamics and chemical kinetics are outlined as background to a discussion of the batch reactor. The characteristic problems of other important reactor types will be taken up in a sequel.     

气体大分子燃料高精度理论热化学研究综述

由于日益严重的能源和环境问题,越来越多的研究者开始致力于提高发动机燃烧性能的研究.研究燃烧化学反应机理的目的是为了精确地预测和控制燃烧过程,从而提高燃烧效率,控制火焰稳定性以及优化排放.对于大分子燃料,通常采用类比的方法来估测其反应速率常数以构建其燃烧反应模型,但是这将会为模型带来较大的计算误差.为了更好地将大分子燃料应用在发动机中,对其进行高精度化学反应动力学研究是十分必要的.但是,由于目前广泛使用的高精度电子结构理论计算方法（如CCSD（T）/CBS和QCISD（T）/CBS）在处理这些大分子燃料上存在着巨大的困难,因此文章关注了目前可适用于大分子体系的高精度量化计算方法,并详细地介绍了其中一种适用于大分子体系的高精度量化计算方法ONIOM[QCISD（T）/CBS:DFT].该方法的提出不仅为研究大分子燃料体系的能量计算提供了准确与可行的计算方法,并有助于得到高精度的反应速率常数,对大分子燃料高精度理论热化学研究具有重要意义.      

Martensitic transformations in a skeleton-type TiC/TiNi composite

The temperature kinetics of martensitic transformations in a skeleton-type TiC/TiNi composite with micron-sized structural constituents was studied. The composite is fabricated using a unique technique. Heat treatment and a change in the chemical composition of the titanium carbide are shown to affect the transformation temperatures. This effect is related to the redistribution of the chemical elements between the carbide and metallic components of the composite; as a result, the titanium nickelide becomes enriched in nickel.     

A rapid,spatially dispersive frequency comb spectrograph aimed at gas phase chemical reaction kinetics

This New Views article will highlight some recent advances in high sensitivity gas detection using direct infrared absorption frequency comb laser spectroscopy, with a focus on frequency comb use in chemical reaction kinetics and our own contribution to this field. Our recently implemented detection technique uses a combination of a 12.9?GHz free spectral range virtually imaged phased array and diffraction grating to spatially disperse the mid-infrared frequency comb onto a camera. Individual frequencies or ‘comb teeth’ of a 250?MHz repetition-rate frequency comb are able to be resolved. High molecular sensitivity is achieved by increasing the interaction path length using a Herriott multipass cell. High spectral resolution, broadband spectral coverage, and high molecular sensitivity are all achieved on an adjustable 1–50 µs timescale, making this frequency comb apparatus ideal for measuring chemical reaction kinetics where multiple absorbing species can be monitored simultaneously. This New Views article will also discuss some of the challenges and decisions that chemists might face in implementing this advanced physics technology in their own laboratory.

Spatially dispersed 250 MHz mid-infrared frequency comb laser, with absorption of some frequencies by a dilute sample of methane.     

Numerical simulation of nonequilibrium flows by using the state-to-state approach in commercial software

Nonequilibrium flows of a two-component oxygen mixture O₂/O behind a shock wave are studied with due allowance for the state-to-state vibrational and chemical kinetics. The system of gas-dynamic equations is supplemented with kinetic equations including contributions of VT (TV)-exchange and dissociation processes. A method of the numerical solution of this system with the use of the ANSYS Fluent commercial software package is proposed, which is used in a combination with the authors’ code that takes into account nonequilibrium kinetics. The computed results are compared with parameters obtained by solving the problem in the shock-fitting formulation. The vibrational temperature is compared with experimental data. The numerical tool proposed in the present paper is applied to study the flow around a cylinder.