微尺度甲烷扩散火焰特性的数值解析

以均匀空气流中圆管形成的甲烷扩散火焰为对象，用数值解析的方法研究了微尺度扩散火焰的火焰结构和燃烧特性．燃烧反应采用甲烷／空气一步总括反应，喷管壁面绝热．在Re一定的情况下，改变喷口尺寸和喷口流速，考察了微扩散火焰的结构和火焰熄灭的尺度效应．计算结果表明，Re=12条件下，喷口直径为0．07mm时达到熄灭极限；稳定燃烧区的最小总放热率约为0．5W；微尺度条件下，Da对火焰结构和火焰熄灭有显著影响，熄火附近的Da的数量级在0．01．     

钝体驻定湍流扩散火焰局部熄火的PDF模拟

用标量联合的概率密度函数(PDF)方法对钝体驻定的湍流射流扩散Sydney火焰HM3进行数值模拟,速度场用一个修正的LRR-IP雷诺应力模型求解.采用3种不同层次的甲烷反应动力学机理对火焰的宏观结构和熄火特征进行比较研究,并结合当地自适应建表方法加速化学反应计算.结果表明,计算值和实验数据吻合较好,在回流区内,不同反应机理的预测值差别不大,但在颈部区域,C2机理相对C1机理可以更准确地模拟标量场的变化和局部熄火现象.     

采用考虑详细化学反应机理的火焰面模型模拟湍流扩散火焰

采用详细的甲烷氧化化学反应动力学机理(GRI-Mech3．0)对不同拉伸率条件下的拉伸层流扩散火焰面结构进行了数值计算，建立了一个包含一系列拉伸层流火焰面结构的火焰面数据库．将这些层流火焰面结构和美国Sandia国家实验室测得的湍流扩散火焰(FlameD)的平均火焰结构进行了对比，发现层流火焰面所覆盖的范围基本包含了所考虑的湍流火焰中不同位置的平均火焰结构，这表明火焰面模型是合理的．然后，采用火焰面模型对该湍流扩散火焰进行了数值模拟并和实验数据进行了比较，考察了火焰面模型的精确程度和模拟深度.     

细水雾抑制气体扩散火焰的机理研究

应用三维LDV／APV系统和热成像方法,测量了细水雾和气体扩散火焰作用过程中的细水雾雾场、火焰温度场并研究了细水雾和气体扩散火焰的作用过程．探索了细水雾抑制火焰的机理和规律,比较了细水雾抑制气体扩散火焰时3种主要灭火机理,用数据定量表征了细水雾灭火时,水雾的蒸发潜热吸热作用、热容吸热作用以及稀释氧气作用对抑制气体扩散火焰所做的贡献,细水雾直接喷射或被卷吸进入火焰内部时,由于表面积大,吸收热量快,迅速汽化,体积扩大。大量的汽化潜热会降低火焰区及气相燃料的温度,细水雾及其蒸汽吸收部分热辐射,降低对燃料的热回馈,减少其汽化蒸发,从而降低反应区的可燃气体积分量。这些因素都会大大降低化学反应速度,抑制火灾的发展,直至扑灭火灾。     

基于化学爆炸模式分析方法的二甲醚对冲扩散火焰中NOx排放机理研究

研究了化学爆炸模式分析（CEMA）方法在NO_x排放机理中的应用及可行性,揭示了主导NO_x排放路径的作用机理,并确定了NO_x排放的关键反应动力学因素。结果表明：CEMA方法可以准确表征NO_x排放路径;在化学当量等值面,基元反应R309（N+NO=N₂+O）和R371（CH+N₂=HCN+N）分别在低、高全局拉伸率下对NO_x的排放影响最显著,减小其反应速率能极大地控制NO_x的排放量。     

湍流预混对冲火焰结构及熄火特性试验研究

利用激光层析技术和数字图像处理技术对对冲方式下湍流预混火焰的结构及熄火特性进行了试验研究。采用PIV方法测量了冷态对冲面附近的速度场,获得了速度作为衡量流场对锋面燃烧影响的参数。在不同射流工况配置下（Reynolds数,全局应变率,燃料的化学混合当量,不对称动量）,观察到随着湍流对冲强度的提高,在高度皱褶的火焰锋面上存在非连续突触和空洞,这是局部熄火的表现,这些局部熄火点影响的扩展会导致火焰的整体熄火。此观点通过局部火焰锋面曲率的概率统计分析得到支持。另外,获得的在火焰熄火的极限条件下,对实际燃烧器的设计有指导意义。     

湍流扩散火焰中对基于混合分数的湍流燃烧模型的数值研究

根据条件矩模型(CMC)和小火焰面模型在模型构建上的相似,针对具有不同大小雷诺数和湍流-化学相互作用特性的非预混湍流射流火焰,对这两种模型进行了数值研究和比较.湍流燃烧模型采用Lagrangian型非稳态小火焰模型(LFM)和径向加权积分的CMC模型,而在H2/N2火焰的数值研究中还考虑了稳态小火焰模型的数值模拟结果....     

二甲醚火焰传播速度的实验研究

用对冲火焰法测量了二甲醚的层流火焰传播速度．在室温和常压下得到了当量比为0．76～1．76的火焰速度,并与文献中其他方法测量得到的结果进行了比较,表明本实验所得二甲醚的火焰传播速度相对更为合理．实验得到二甲醚的火焰传播速度最大值约为54cm／s．     

固定磁场对油池扩散火焰烟尘特性和火焰形状影响的研究

通过理论分析和实验研究,得到了固定磁场作用下火焰的烟尘和形状特性随磁感应强度变化的关系。对于油池扩散火焰,当其在固定磁场的作用下,火焰中的烟尘份额会随磁感应强度的增加而减小,火焰的温度会有所升高,火焰的形状也会随磁感应强度的变化而发生不同程度的改变,这不仅与磁场的强度有关,而且与火焰本身的燃烧特性也有一定的关系。     

不同扩散效应下一维湍流模拟氢气-空气射流的扩散火焰

应用一维湍流模型（ODT）来研究湍流射流氢气．空气扩散火焰,研究过程中采用详细化学反应机理和多分量输运属性．对于火焰长度、主要燃烧产物及温度的预测较好地符合了实验结果．ODT模拟结果产生了较高的近场扰动．提出了一种旨在通过修改涡事件选择过程从而提高ODT模型精度的新观点．在模拟中检验了微分扩散效应,结果显示当前火焰中存在着显著不同的扩散效应．     

Turbulent diffusion combustion model using chemical equilibrium combined with the eddy dissipation concept for reducing detailed chemical mechanisms: An application of H2‐air turbulent diffusion flame

This research aims at building a turbulent diffusion combustion model based on chemical equilibrium and kinetics for simplifying a complex chemical mechanism. This paper presents the combustion model based on chemical equilibrium combined with an eddy dissipation concept model (CE‐EDC); the model is validated by simulating a H₂‐air turbulent diffusion flame. In the CE‐EDC model, the reaction rate of fuels and intermediate species are estimated by using the equations of the EDC model. Then, the reacted fuels and intermediate species are assumed to be in chemical equilibrium; the amounts of the other species are determined by the Gibbs free energy minimization method by using the amounts of the reacted fuels, intermediate species, and air as reactants. An advantage of the CE‐EDC model is that the amounts of the combustion products can be determined without using detailed chemical mechanisms. Moreover, it can also predict the amounts of the intermediate species. The obtained results are compared with Takagi's experimental data and the data computed by the EDC model, which uses the complex chemical mechanisms. The mole fractions of H₂, O₂, H₂O, temperature, and velocity obtained by using our CE‐EDC model were in good agreement with the reference data without taking into account the chemical reaction rates of the O₂ and H₂O. Furthermore, the mole fractions of OH and H are in good agreement with the results of the EDC model at high temperatures. On the other hand, the chemical equations involving OH and H were used for predicting the mole fractions of OH and H, which were similar to those obtained from the EDC model at low temperatures. Using the present CE‐EDC model, amounts of combustion products can be calculated by using a reduced chemical mechanism and the Gibbs free energy minimization theory. The accuracy of this model is in the same order as that of the EDC model. The CE‐EDC model uses reduced chemical mechanism concerning selected species, while the result of the chemical equilibrium calculation was employed to the other species; further, the accuracy of the CE‐EDC model is the same as that of the EDC model as to major species, T, U, and k. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20296     

TiO2纳米颗粒在火焰中凝结长大的数值模拟

颗粒生长的数值模拟是通过流体动力学与颗粒动力学相结合计算实现的.实验表明,温度是颗粒成长中非常重要的因素之一,所以湍流扩散火焰的正确模拟,是颗粒学模型计算结果正确与否的关键.首先在CFD商业软件FLUENT中计算得到准确的丙烷与空气、四氯化钛与空气反应的湍流火焰场;然后应用FLUENT的UDF功能,编制C语言程序引入颗粒学模型进行计算,对颗粒尺寸进行了预测;通过对计算结果的分析探讨火焰温度、氧化剂流量等因素对生成颗粒或者颗粒聚集块尺寸的影响.结果表明:空气流率对火焰场温度影响很大;火焰场温度越高就越容易形成球形颗粒;颗粒在火焰中的时间越长,生成的颗粒或聚集块的尺寸就越大;气体的稀释作用对颗粒成长有一定影响.     

CFD simulation for turbulent mixing with the stochastic approach

A computational fluid‐dynamic simulation for a turbulent nonuniform combustion is established using a stochastic approach. At each point in a turbulent flow field, the variations of species mass fraction and temperature are statistically described by the joint‐probability density function (pdf), and the velocity variation is expressed using the conventional k–? turbulent model. The transport equation of this joint pdf of mass fraction and temperature is calculated by a finite‐difference method in convection and turbulent diffusion and by the Curl collision‐redispersion model in molecular mixing. This method is applied to simulate the process of scalar dispersion in a uniform isotropic turbulent flow. The results show that the profile of an averaged scalar is quite similar to those calculated using conventional transport equations. Furthermore, a reasonable degree of reproduction is achieved for the pdfs of the scalar at each point in the flow field. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 503–511, 2001     

基于CFD的天然气管道混气扩散规律研究

随着我国多气源天然气市场发展和整体供气管网的形成,多气源直接接入管网混输已成为必然,不同气质气源直接管道混气的技术问题亟待研究和解决。基于CFD模拟,对不同气源混合输运的气质扩散规律进行研究,为混输管网合理设计和准确设定气质监控点提供依据,以保证燃气管网系统的安全可靠运行。重点对典型混气管路(Y型管)的天然气气质扩散规律进行数值模拟,获得掺混流体剪切层质量传递特征和天然气气质扩散规律。根据混气湍流形态和浓度场分布特征,获得Y型管的三类混气类型。通过对气质扩散浓度的不均匀性理论分析和模拟结果的综合数据分析,建立了预测混气管道达到气质均匀的混合长度无因次准则方程,为工程设计提供理论方法和计算基础。     

液体火箭发动机燃烧稳定性CFD分析

应用CFD方法对液体火箭发动机中的高频燃烧不稳定性进行了分析研究,建立了液体火箭发动机不稳定燃烧数值模拟的综合模型和控制方程,比较了PISO和MacCormack两种算法,得出了两种算法均能成功应用于不稳定燃烧分析的结论。阐述了ACLRECI系列程序。应用该程序对YF－860液氢液氧发动机和NAL液氧／甲烷发动机的稳定性进行了数值模拟,得出了该发动机的燃烧稳定性极限图。数值计算结果与试车数据一致。     

220t／h CFB锅炉旋风分离器性能的数值模拟研究

旋风分离器是循环流化床（简称CFB）锅炉的关键部件之一,基于数值模拟计算,研究了220t／h节能环保型CFB锅炉旋风分离器结构对气固流动的影响,提出了改进和完善分离器效率的方法,对于CFB锅炉高效旋风分离器的研制具有重要参考意义。     

A finite volume method on distorted quadrilateral meshes for discretization of the energy equation's conduction term

A finite volume method (FVM) on distorted meshes for discretizing the energy equation's conduction term is presented. In this method, it is possible to compose the computational mesh of general quadrilateral elements (cells), namely, the cells are not required to be rectangular. The gradient of temperature on the cell's surface is computed to be second‐order accurate. Therefore, the error of numerical results by this method is smaller than using the traditional multilateral element method (MEM). The error does not depend on the degree of mesh distortion. The formulation based only on Taylor's theorem is straightforward. These are advantageous features to revise the fluid flow computation programs (based on FVM) that neglected the heat conduction term of the energy equation. The test calculations show that the convergence tendency of the numerical error using this method with the distorted mesh is the same as using an ordinary 2‐node central difference scheme on a constant‐interval rectangular mesh. By this method a conduction term was added to the energy equation of a SALE [ 1 ] program which had neglected that term originally, and z numerical calculation of a fluid flow with a heat transfer problem was performed. The numerical result of the present method with the distorted mesh well agrees with the analytical solution and the result of REM with a rectangular mesh. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20375