湍流脉动对自由火焰温度场反演的影响

发射-透射方法是火焰温度测量的一种重要方法。相对于湍流脉动的时间尺度而言,火焰红外光谱测量中探测器的时间分辨率一般较低。本文用迭代法分析了轴对称自由火焰温度的发射-透射测量中湍流脉动对温度场反演的影响。用简化的概率密度函数模拟温度和吸收系数的脉动。分析结果表明,在湍流脉动微弱的情况下,湍流脉动对时均温度场的反演影响很小,但在强湍流脉动的情况下湍流脉动对时均温度场的反演有很大影响。     

网格湍流对剪切层中预混火焰结构的影响

本文研究网格湍流对射流剪切层以及建立在其中的预混火焰的影响。利用热线风速仪测量射流的速度场,发现网格湍流使剪切层内湍流强度明显降低,抑制了低频速度脉动,同时增加了湍动能在小尺度脉动上的分配,使湍流更趋于各向同性,这表明网格湍流抑制了剪切层内的大涡和拟序结构。用细丝热电偶测量了火焰温度,结果显示网格湍流使火焰前峰的低频大幅摆动减少,小尺度皱褶增加,火焰区平均温度更高,说明网格湍流有利于剪切层中预混火焰的强化和稳定。     

湍流和预混火焰相互作用的实验研究

建立了湍流预混火焰实验系统并实现了驻定火焰。无条件示踪条件下的研究结果表明,火焰区的速度分布呈现 双峰分布,初步证实火焰区湍流度峰值的存在是由于火焰脉动导致速度测值分散,最终由统计得到表观湍流度的增大。条 件示踪测量结果表明,在火焰区反应物来流的湍流度与上游的测值并没有明显的变化,进一步证实了这一结论。     

湍流对多孔介质内预混火焰影响的初步研究

当气流速度较大时,多孔介质内预混燃烧的模拟需要考虑湍流的影响,本文利用简化的k-ε双方程湍流反应流模型对多孔介质内的预混火焰进行了数值模拟.结果表明,湍流大大加强了气流的组分和能世扩散,计算得到的火焰传播速度、CO及NO的排放量都与实验值符合得比较好,与层流模型相比,湍流模型能够改善计算结果.     

受限湍流射流扩散火焰的PDF模拟

采用k-ε双方程模型和概率密度函数(PDF)相结合的办法,研究受限条件下的湍流射流扩散火焰,着重考虑受限条件下固体壁面、压力梯度等因素对速度场和标量场求解的影响,并在此基础上对两个不同尺寸的受限湍流燃烧场进行计算,分别研究了受限湍流射流扩散火焰的流场结构、火焰结构和火焰形状.最后给出结果,定性分析,并得出结论.     

基于FGM的湍流射流扩散火焰超大涡模拟

为了研究超大涡模拟(VLES)预测湍流燃烧问题的能力,本文采用VLES结合基于假定概率密度函数的火焰面生成流型(FGM)建表湍流燃烧模型对值班甲烷/空气湍流射流扩散火焰(Sandia Flame D)开展了高精度数值研究,并与实验结果进行了详细比较。结果表明本文发展的VLES-FGM方法可以较准确地预测出湍流射流扩散火焰中的非稳态燃烧过程,且VLES湍流模拟方法对于湍流燃烧问题具有较大的应用潜力。     

湍流预混火焰传播速度的分形模型研究

本文利用激光层析技术和数字图像处理技术,在对Ｒｅｄ＝４３３５～１１１００范围内的Ｂｕｎｓｅｎ式湍流预混火焰热图像序列进行分形分析的基础上,提出了一种基于分形理论的湍流预混火焰传播速度模型,该模型将小尺度涡团在火焰锋面的强化湍流扩散效应归结为对锋面结构的改变上。结果表明：利用该模型预测的火焰传播速度与试验结果基本吻合。     

湍流扩散火焰的非稳态火焰面模拟

采用稳态的和非稳态的火焰面模型同时对一个湍流甲烷射流扩散火焰进行了数值模拟,比较了两者对湍流平均火焰结构、活性自由基和污染物(氮氧化物)排放的模拟效果。速度场采用κ-ε模型计算,守恒标量混合物分数的分布通过其概率密度函数(PDF)输运方程的求解得到。稳态的火焰面结构由查询火焰面数据库得到,而非稳态的火焰面结构由火焰面方程和流场方程耦合求解来计算。采用详细的GRI—Mech 3.0机理描述甲烷的氧化和氮氧化物的形成。数值模拟结果和实验数据作了广泛的对比,验证了火焰面模型对湍流扩散燃烧的定量模拟能力。     

稀甲烷/氢气预混湍流传播火焰实验研究

本文采用定容湍流燃烧弹获取了稀甲烷/氢气/空气在强湍流条件下的火焰发展历程,研究了湍流火焰在负马克斯坦数条件下的传播特性.结果表明,湍流火焰呈现自相似传播特性,即使在强湍流条件下,湍流传播火焰仍然会受到不稳定性的影响.并且随着马克斯坦数的减小,不稳定性对湍流传播火焰的影响增强。同时,本文获得一种新的湍流燃烧速度拟合公式,包含了负马克斯坦数条件下不稳定性对湍流燃烧速度的影响。     

湍流预混火焰的时间和空间分形特性研究

1引言湍流燃烧过程是一个强烈的非线性动力学过程，用于描述湍流燃烧的诸多特性参数表现出随机脉动的特点，对于传统参量的分析处理也只能停留在时均平均加脉动项的概率统计上，不论从时间、还是空间角度都显粗糙。Damkohler[1]早在1942年提出了火焰结构与湍流燃烧速度的内在联系，引导人们将注意力转向火焰形状结构的研究上。图像计算机技术的兴起为实时获得湍流火焰结构参数创造了条件。Boyer[2]在研究高强度湍流燃烧时发现，由于脉动造成的复杂火焰表面已不能用传统的Euclidean几何加以描述。分形理论不仅可以用细微尺度规划几何结构，…     

Fluctuating characteristics of radiative source term in hydrogen turbulent jet diffusion flame

The laminar flamelet model in combination with joint probability density function transport equation of mixture fraction and turbulence frequency is used to simulate turbulent jet diffusion flames of hydrogen. The frequency distributions of radiative source terms are calculated for four important infrared bands of water vapor. The results show that, for the given ensemble, about 95% samples of radiative source term for each band locate within the region of ±3.0 standard deviation of the mean radiative source term. Due to the different relation between band intensity parameters and temperature for every band, the symmetrization of frequency distributions for each band is different.     

Application of multi-phase particle swarm optimization technique to inverse radiation problem

The multi-phase particle swarm optimization (MPPSO) technique is applied to the inverse radiation problem in the present paper. The directional radiative intensities are served as the measurement data to estimate the radiative source term, optical thickness, scattering albedo, and phase function in one-dimensional semitransparent plane-parallel media by the inverse simulation. To check the performance and accuracy in retrieval, a comparison is presented between three PSO methods, i.e. the MPPSO, the standard PSO, and the Stochastic PSO. The results confirm the potential of the proposed approach MPPSO and show its effectiveness and superiority over the other two PSO algorithms. Furthermore, the effects of swarm size, searching space, phase change frequency, and velocity-reinitializing frequency on the convergence velocity and computational accuracy of MPPSO are also investigated.     

轴对称介质内辐射源项反演算法

结合Abel变换和离散坐标法,提出了一种基于CCD相机采集的单幅辐射图像重建轴对称发射-吸收介质内辐射源项分布的反演算法。通过在求解辐射正问题得到的准确值的基础上,添加随机噪声模拟试验测量数据,分析了网格数目、辐射源项分布形式、吸收系数和测量误差对算法反演精度的影响。测试结果表明:该算法对测量误差不敏感,在有测量误差的情况下也能够准确的重建介质内的辐射源项分布。     

Transient coupled radiation-conduction in infinite semitransparent cylinders

A method is developed to analyze the transient coupled radiation-conduction in infinite semitransparent cylinders surrounded by isothermal black walls. The radiative heat source term is calculated by the radiative transfer coefficients and the transient energy equation is solved by an implicit finite difference method. The radiative transfer coefficients are deduced by use of the ray tracing method in combination with the Hottel and Sarofim zonal method. The effects of the related parameters on the transient radiative heat source and temperature distribution are analyzed. It is found that the peak of the dimensionless radial radiative heat source can be located at the interior shell of the cylinder with small optical thickness when heated by the surrounding irradiation. Treating the volume radiation as a surface radiation will result in large errors of transient temperature distribution for the cylinder with small optical thickness.     

用射线踪迹法解黑表面矩形介质耦合换热

本文用射线踪迹-节点分析法研究了二维黑体表面矩形、各向同性散射半透明介质内辐射与导热瞬态耦合换热。采用全隐格式的有限差分法离散二维瞬态微分能量方程,用辐射传递系数来表示辐射源项,结合谱带模型并采用射线踪迹法求解辐射传递系数。采用Patankar线性化方法将辐射源项及不透明边界条件线性化,并采用附加源项法处理边界条件,运用ADI方法求解名以上的线性化方程组,从而解得二维矩形介质内的瞬态温度分布。     

An inverse source problem in radiative transfer

The spherical-harmonics method is used to develop a solution to an inverse source problem in radiative transfer. It is assumed that, with the exception of the inhomogeneous source term, all aspects of the radiation-transport problem are known, and we seek to determine the inhomogeneous source term from specified angular distributions of radiation exiting the two surfaces of a homogeneous plane-parallel medium. Anisotropic scattering is included in the monochromatic radiative-transfer model and general reflecting boundary conditions are considered.     

Transient coupled heat transfer in a rectangular medium with black surfaces

The main objective of this paper is to extend to two-dimensional (2-D) medium the ray tracing-node analyzing method, which has already been successfully used to solve one-dimensional (1-D) problem of coupled heat transfer in a semitransparent medium. For simplicity, an infinitely long rectangular semitransparent medium with four black opaque surfaces is chosen as our studying object. A control volume method in the implicit scheme is adopted for discretizing the partial transient energy equation. In combination with spectral band model, the radiative heat source term is calculated using the radiative transfer coefficients (RTCs), which are deduced by the ray tracing method. The Partankar's linearization method is used to linearize the radiative source term and the opaque boundary condition, and the linearized equations are solved by the ADI method. Effects of absorption coefficient, refractive index and conductivity on transient cooling process in the 2-D gray rectangular medium are investigated under the condition that the radiation and convection processes cool one side of the rectangular medium while heat the remaining three sides.     

多孔介质预混燃烧中辐射属性影响的敏感性分析

建立了惰性多孔介质中预混合燃烧的数学模型,采用辐射传递的有限体积法求解固相能量方程中的辐射源项,研究多孔介质热辐射在燃烧系统中的作用,考察辐射属性(吸收系数和散射反照率)对轴向温度场和辐射热流量影响的敏感性。研究表明,辐射属性参数波动对预测结果影响明显,固体热辐射在多孔介质预混燃烧中的影响不可忽略。     

A concept of multi-scale modeling for radiative heat transfer in particle polydispersions

To take the local thermal nonequilibrium between particles and the nonuniformity of temperature within a single particle into account, a concept of multi-scale modeling of radiative transfer is presented. Particles are considered to interact with thermal radiation on both micro-scale of a single particle and meso-scale of a particle cell to produce radiative source term at the local or meso-scale level of a particle cell for the modeling of radiative transfer at macro-scale of overall particle system. The accurate modeling of radiative transfer in particle polydispersions are related to the modeling of radiative transfer in following three different scales: macro-scale of the overall particle system, meso-scale of particle cell, and micro-scale of single particle. Two examples are taken to show the necessity of multi-scale modeling for radiative transfer in particle polydispersions. The results show that omitting local thermal nonequilibrium and nonuniformity will result in errors for the solution of radiative heat transfer to some extent, and the multi-scale modeling is necessary for the radiative transfer in particle system with large local thermal nonequilibrium and nonuniformity.     

气粒混合物非灰辐射特性合并宽窄谱带K分布模型

气粒混合物辐射问题具有全场性、非灰性、耦合性等特点,准确预估高温燃气/粒子非灰辐射特性是非常重要的。本文将合并宽窄谱带K分布模础(CWNBCK)与离散坐标法(DOM)结合,开展了非灰气粒混合物辐射换热问题的模拟工作,分别验证了一维和三维情况下应用该模型的准确性,给出不同工况下的热流源项、壁面热流或辐射热流等。结果表明:该模型能够给出与SNB模型精度基本相同的结果,考虑其计算效率的提高,可以在工程实际中应用该模型计算非灰气粒混合物辐射换热。