基于粒子的湍流燃烧火焰的可视化研究

引入粒子系统作为可视化建模的基本方法,建立了包含火焰粒子子模型、湍流流场子模型和燃料属性子模型的湍流燃烧火焰可视化模型.通过将温度场与湍流流场的有机结合及燃烧室内网格体单元的颜色与透明度的显示,实现了湍流燃烧火焰的三维动态传播可视化.最后,结合实例给出了火焰效果图,体现了湍流涡对火焰前锋面的影响.     

基于BP神经网络锅炉炉膛火焰可视化监测方法研究

为了可视化监测炉膛火焰燃烧状况,提出一种基于级联前向BP神经网络模型的锅炉炉膛火焰可视化监测方法。通过比较选取级联前向BP神经网络作为炉膛温度预测模型,利用图像处理技术得到炉膛火焰辐射能图像对应二维温度场,并采用正则化方法重建炉膛火焰三维温度场。仿真结果表明,根据二维温度场可得火焰等温线走向和分布,根据三维温度场易得火焰中心分布及全炉最高温度点信息,实现锅炉运行控制和异常温度报警,满足燃烧诊断要求并实现炉膛火焰可视化监测。     

基于K-means和颜色模型的林火辨识方法研究

为了确保火灾探测结果的可靠性和准确性,从林火燃烧时火焰和烟雾特征出发,对现有的林火探测技术进行了分析,提出了一种基于K-means和颜色模型的林火辨识方法。首先使用Kmeans算法对采集到的彩色图像进行分割,根据火灾发生时火焰和烟雾的颜色特征,采取一种改进的颜色模型对分割出来的子图像进行辨识,对疑似火焰子图像和疑似烟雾子图像进行初步确认,然后从疑似子图像中提取出火焰和烟雾的特征输入到RBF神经网络,判断是否确实发生火灾。     

自然燃烧火焰的快速仿真

从自然燃烧的火焰的现象出发,采用面向对象的方法,提出了一种基于粒子系统的自然燃烧的火焰的快速数值模拟算法.首先,讨论了形成火焰燃烧的动态场景图像的基本原理,给出了火焰图像与背景图融合的算法,并建立了用于火焰仿真的两种火焰颜色模型.然后,建立了用于火焰仿真的火焰粒子、火苗与火焰系统的面向对象模型,给出了各对象的燃烧行为的快速模拟方法.接着,对实现动感火焰的方法进行了讨论,指出了算法.最后给出了通过该文算法进行模拟实验的效果图.该算法准确度较高,速度快,效果较好.     

基于Web的火焰图象处理和燃烧诊断系统的设计与实现

为了实现电站锅炉炉膛火焰的可视化和对炉膛燃烧状况进行在线智能诊断 ,以便为电站运行人员提供有效的运行指导信息 ,研制开发了一套基于 Web的火焰图象处理和燃烧诊断系统 ,并提出了一种采用 Java技术、基于 Web应用的浏览器 /服务器 (B/ S) 3层结构模型 ,同时分析了 B/ S 3层结构的优点 ,并将此结构应用于电站锅炉火焰图象处理和燃烧诊断系统中 .该系统首先通过光学镜头组、CCD摄像机、图象采集卡得到火焰图象 ,同时利用获得的炉内辐射信息来对炉内火焰燃烧状态和 NOX排放量进行在线监控和分析 ;然后根据比色测温原理计算投影温度场 ;最后利用代数重建算法 ART(Algebraic Reconstruction Techniques)来进行燃烧温度场的重建 ,并生成了各种分析曲线图表 .该基于 Web的火焰图象处理和燃烧诊断系统已经在 30 0 MW电站煤粉锅炉上得到初步应用 ,实践证明 ,该系统能够有效地提高电厂运行的经济性和安全性 .     

湍流燃烧反应数值模拟的研究与实现

基于开源计算流体力学平台OpenFOAM和化学动力反应模型库Cantera设计出定常可压缩的湍流燃烧反应解算器,使用该解算器对Sydney钝体驻定火焰HM1进行数值模拟,模拟采用煤气和空气的详细反应机理,并根据计算结果得到燃烧流动组分浓度分布图和温度曲线变化图.通过计算结果与实验数据对比分析表明,模拟效果较好的符合燃烧组分变化的研究要求,这说明设计的解算器对定长可压缩燃烧流动问题有很好的计算仿真效果,体现了其可行性.湍流燃烧流动解算器的设计对于燃烧室性能预估有一定的参考价值.     

基于DGX-2的湍流燃烧问题优化研究

湍流燃烧问题的数值模拟是航空发动机设计的关键工具.由于需要使用高精度计算模型求解NS方程,湍流燃烧的数值模拟需要庞大的计算量,而物理化学模型的引入则导致流场极为复杂,使得计算域内的负载平衡问题成为大规模并行计算的瓶颈.为此文中将湍流燃烧的数值模拟方法在单台具有强大计算能力的服务器——DGX-2上进行移植和优化,设计了通量计算的线程分配方式,并以Roofline模型为工具分析指导了实际的优化方向.此外,还设计了高效的数据通信方式,并结合DGX-2的高速互联实现了湍流燃烧数值模拟方法的多GPU并行版本.实验结果表明,相较于双路Intel Xeon 6248 CPU 40核心的并行版本,迭代过程的计算部分在单块V100上获得了8.1倍的性能提升,在DGX-2共16块V100上达到了66.1倍的加速,优于CPU并行版本所能达到的最高性能.     

钢厂热风炉燃烧控制模型的开发与应用

针对热风炉燃烧系统的复杂性、参数不确定性和非线性,以及某钢厂热风炉燃烧控制过程存在的问题。结合国内外操作经验，在分析拱顶温度变化与最佳空燃比关系、废气温度变化与煤气流量关系的基础上，开发了基于模糊控制的热风炉燃烧控制模型。应用结果表明,该模型的应用实现了燃烧过程的自动控制．提高了热交换效率，节约能源．易于实现。     

发光火焰二维温度分布的实时测量

分布。火焰的温度分布是燃烧检测中既重要又困难的课题。本文以数字图象处理技术为手段,把定性分析与定量计算结合起来,通过实验求取测温模型,再对发光火焰图象信息进行处理和计算,以获取其温度和温度分布。     

航空发动机加力火焰检测的试验验证

为了准确获取航空发动机加力燃烧室火焰燃烧情况进行推力控制，针对航空发动机控制系统中加力火焰检测的作用，分析了基于离子火焰传感器的加力火焰检测工作原理。根据离子火焰传感器在航空发动机中的实际安装情况，分析提出了影响加力火焰检测的因素，包括离子电流的汇流面形状、离子火焰传感器电极与汇流面的相对距离、燃烧温度以及离子火焰传感器电缆的寄生电容。通过搭建燃烧试验平台进行试验，验证了离子火焰传感器在航空发动机实际安装使用中各影响因素对离子火焰传感器采集值影响趋势，试验结果可用于航空发动机加力状态检测相关故障的排查。     

Level Set Curve Matching and Particle Image Velocimetry for Resolving Chemistry and Turbulence Interactions in Propagating Flames

We present an imaging, image processing, and image analysis framework for facilitating the separation of flow and chemistry effects on local flame front structures. Image data of combustion processes are obtained by a novel technique that combines simultaneous measurements of distribution evolutions of OH radicals and of instantaneous velocity fields in turbulent flames. High-speed planar laser induced fluorescence (PLIF) of OH radicals is used to track the response of the flame front to the turbulent flow field. Instantaneous velocity field measurements are simultaneously performed using particle image velocimetry (PIV). Image analysis methods are developed to process the experimentally captured data for the quantitative study of turbulence/chemistry interactions. The flame image sequences are smoothed using nonlinear diffusion filtering and flame boundary contours are automatically segmented using active contour models. OH image sequences are analyzed using a curve matching algorithm that incorporates level sets and geodesic path computation to track the propagation of curves representing successive flame contours within a sequence. This makes it possible to calculate local flame front velocities, which are strongly affected by turbulence/chemistry interactions. Since the PIV data resolves the turbulent flow field, the combined technique allows a more detailed investigation of turbulent flame phenomena.     

Simulation of combustion by vortex method

In this paper, we present a simple and efficient technique that uses a vortex method to predict the quantities of the combustion products; however, this technique uses no chemical equations. This technique incorporates the concept of chemical equilibrium into a vortex method. By using this technique, the products of a chemical system are determined by minimizing the Gibbs free energy, which is subject to the conservation of the chemical elements involved in the combustion process. The amount of gas (a mixture of fuel and oxygen) that is used for the calculation of chemical equilibrium is estimated by the eddy-dissipation model. In order to avoid increasing the number of species of particles, a single particle is provided with five physical properties - vorticity, turbulent energy, dissipation rate, amount of fuel, and amount of oxygen. To meet this condition, the motion equations of these properties are modified. For the sake of simplicity and low computational load, the presented technique does not focus on achieving higher order accuracy in the solutions. Nevertheless, the simulated results for the temperature and the main products for the premixed methane/air jet turbulent flame are in good agreement with the experimental results. In some cases, the data from the simulation concerning the intermediate products disagree with that from the experiment due to the slow reaction speeds in actual combustion. The convergence of the algorithms is also examined.     

隧道内细水雾抑制火灾事故的数值仿真

以工业灾害的抑制技术为背景,针对隧道内发生的火灾事故,采用数值仿真技术研究连续喷射水雾阻挡气相物质燃烧的过程.并讨论水雾抑制燃烧的机理.相比于欧拉/欧拉方法,欧拉/拉格朗日方法能较好地描述水雾液滴引起的瞬时流动特性及变化经历,利用欧拉/拉格朗日方法,对气相反应流及水雾扩散过程进行数值研究.应用颗粒随机轨道模型,来考察湍流对水雾液滴扩散的影响.比较了有、无水雾抑制时和水雾不同初始流量下,隧道内流场的温度分布情况,揭示了水雾液滴的运动特性,为火灾事故抑制技术的发展提供理论依据.     

Experimental and numerical modeling of the effect of solid surface on NOx emission in the combustion chamber of a water heater

A combined experimental and CFD modeling study of the turbulent non-premixed natural gas on a laboratory scale has been performed. Effect of solid surface enhancement in combustion chamber on the flame temperature and NO emission was investigated. The solid surface called as filling material (FM) was cylindrical and was placed coaxially in the center of combustion chamber. The temperature and NO distribution in the combustion chamber were compared for different geometries of the filling material. The diameters of the filling materials were 25 and 30 cm with two lengths of 20 and 40 cm. Experimental study has been carried out on a fire tube water heater. The flame temperature on the center line of the combustion chamber, gas temperature and NO emission in the combustion chamber were measured. The actual geometry of the fire tube water heater and the burner were modeled and then analyzed by the FLUENT code. Turbulent diffusion flames were investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The measured values were specified as the boundary conditions. The elemental analysis of the natural gas was taken as a mixture of hydrocarbon and air was the oxidizer. The standard k-ε model was used for the modeling of the turbulence phenomena in the combustor. The non-premixed combustion model was chosen. In the conserved scalar approach, turbulence effects were accounted for with the help of an assumed shape probability density function or PDF. The discrete ordinates (DO) radiation model was used for modeling of the radiative heat transfer in the combustion room. The model results were compared with the experimental results. The model results were in good agreement with the measurements. The filling material provided the recirculation of the cooler gases into the flame. The recirculation reduced the oxygen concentration in the flame and controlled the flame temperature. It was found that the filling material with the diameter bigger than the flame diameter increased the heat transfer rate in the back flow around the flame.     

Renormalization Group-Based Transport Modeling of Premixed Turbulent Combustion: I. Incompressible Deflagration Model

A new method for numerical modeling of premixed turbulent combustion is introduced based on the thin flame model. Applications are given, e.g., to flames in turbulent flow in channels and over backward facing steps.     

Renormalization Group-Based Transport Modeling of Premixed Turbulent Combustion. II. Finite Density Gradient and Direct Heat Release

A new method for numerical simulation of flame propagation in turbulent premixed combustible gaseous mixtures is proposed and tested. The method combines (I) a modified eikonal equation, employed to model the flame front dynamics; (2) a method of front tracking using a strip of computational cells containing the flame; and (3) a formula for turbulent flame propagation speed. The method includes two separate models. The first one obviates the necessity to solve equations for heat release, temperature and enthalpy, and utilizes a model equation of state to accurately render the volumetric effect and related instabilities. The second one provides a model for direct heal release and temperature calculation in the presence of heat-conducting boundaries (walls), in the multi-component combustible mixtures with variable composition and temperature-dependent heat capacities of all species. This model can be used when the heat transport on the walls is of interest, effects of flame quenching are essential and for the especially important case of combustion in a closed volume, e.g., in a cylinder of an internal combustion engine or chemical reactor. This modification is also effective for simulation of ramjet engines. The new method proves to be self-consistent, robust and highly effective.     

Numerical investigation of erosion threshold velocity in a pipe with sudden contraction

This paper deals with erosion prediction in a pipe with sudden contraction for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration. The pipe axis was considered vertical and the flow was either in direction of gravity (downflow) or against it (upflow). The mathematical models for the calculations of the fluid velocity field and the motion of the solid particles have been established and an erosion model was used to predict the erosion rate. The fluid velocity (continuous phase) model was based on the time-averaged governing equations of 3-D turbulent flow and the particle-tracking model (discrete phase) was based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behavior. The effects of flow velocity and particle size were investigated for one contraction geometry considering water flow in a steel pipe. The results showed the strong dependence of erosion on both particle size and flow velocity but with little dependence on the direction of flow. The effect of flow direction was found to be significant only for large particle size and moderate flow velocity. The erosion critical area was found to be the inner surface of the tube sheet (connecting the two pipes) in the region close to the small pipe. The results also indicated the presence of a threshold velocity below which erosion is insignificant for all particle sizes.     

Visualization of vorticity and vortices in wall-bounded turbulent flows

This study was initiated by the scientifically interesting prospect of applying advanced visualization techniques to gain further insight into various spatio-temporal characteristics of turbulent flows. The ability to study complex kinematical and dynamical features of turbulence provides means of extracting the underlying physics of turbulent fluid motion. The objective is to analyze the use of a vorticity field line approach to study numerically generated incompressible turbulent flows. In order to study the vorticity field, we present a field line animation technique which uses a specialized particle advection and seeding strategy. Efficient analysis is achieved by decoupling the rendering stage from the preceding stages of the visualization method. This allows interactive exploration of multiple fields simultaneously, which sets the stage for a more complete analysis of the flow field. Multifield visualizations are obtained using a flexible volume rendering framework which is presented in this paper. Vorticity field lines have been employed as indicators to provide a means to identify "ejection" and "sweep" regions; two particularly important spatio-temporal events in wall-bounded turbulent flows. Their relation to the rate of turbulent kinetic energy production and viscous dissipation, respectively, have been identified.     

Physics-inspired controllable flame animation

We propose a novel method conceptualized from the properties of physics where in particular the shape of a flame is determined by temperature that enables a control mechanism for the intuitive shaping of a flame. We focused on a trade-off issue from computer graphics whereby the turbulent flow that expresses the characteristics of the flame has a tendency to shift continuously, whereas the velocity constraints that contain a fluid within a target shape have a tendency to force movement in a particular direction. Trade-off made it difficult for animation designers to maintain a flame within the intended target shape. This paper resolves the issue by enabling the flame to be controlled without any velocity constraints by using the following two techniques: First, we model the temperature and force of the explosion generated by the combustion of explosive gaseous fuel and apply it to certain regions. Second, we expand the space of the interface between the fuel and the burned products, classifying that space into four regions and controlling the target shape of the flame by delicate adjustments to the temperature in each region. Experiments show that the flame maintains the appearance of dynamic movement while preserving the detailed 3D shapes specified by the scene designers.