湍流预混和分层燃烧中亚格子模型研究及其在大涡模拟中的应用
发布时间：2018-09-10 06:19
【摘要】：低污染物排放的燃烧室设计要求促进了贫燃预混燃烧技术在燃气轮机和航空发动机中的应用。与非预混燃烧相比,贫燃预混燃烧能够降低燃烧室内峰值温度,进而有效降低NO_x排放。在实际燃烧室内,空间和时间的约束影响了燃料和氧化剂之间的预混程度,导致预混气体的当量比在空间呈现梯度,进而出现分层燃烧。为了有效预测复杂流场结构、燃烧过程中非定常现象以及湍流涡旋与火焰复杂的相互作用,大涡模拟方法得到了广泛应用。湍流燃烧大涡模拟的主要困难在于非线性的多尺度湍流和多尺度化学反应的相互耦合,导致化学反应源项模化及方程求解难度很大。本文紧紧围绕湍流预混和分层火焰,发展了若干亚格子模型,并针对不同流场工况、不同驻定机制以及不同燃烧机制的若干典型湍流燃烧算例开展了大涡模拟研究。主要工作及创新点如下:首先,对剑桥旋流燃烧器的冷态流场进行了大涡模拟研究。大涡模拟统计结果与实验结果符合较好,验证了数值方法的准确性。在燃烧器出口的剪切层附近,采用Q准则识别了无旋流工况的环状涡结构和有旋流工况的螺旋涡结构。基于功率谱密度分析了涡旋脱落的发生,以及进动涡核的存在导致流场的振荡现象。采用三维本征正交分解提取了有旋流动中大尺度结构,预测了多种流动不稳定现象,包括涡旋脱落、进动涡核和钝体回流区末端的不稳定性。其次,基于详细化学建表结合假定概率密度函数的亚格子模型,对高Karlovitz数的值班预混射流火焰开展了大涡模拟研究。采用自点火模型耦合预混火焰传播模型构建详细化学热力学表。计算了不同未燃气体温度条件下一维非稳态的层流预混火焰,对耦合建表方法预测化学热力学状态的能力进行了评估。使用假定概率密度函数考虑湍流和化学反应之间的相互作用,其中假定双混合物分数的概率密度分布为Dirichlet分布。探讨了不同详细化学建表方法和不同假定概率密度函数模型对计算结果的影响,然后分析了高Karlovitz数的值班预混射流火焰的流场结构和火焰结构。再者,基于动态加厚火焰结合火焰面生成流形建表方法的亚格子模型(DTF-FGM),对薄反应机制下湍流预混和分层火焰开展了大涡模拟研究。利用反应进度变量定义的火焰指数动态确定加厚因子,使得加厚过程限制在实际计算需要加厚的区域。针对湍流预混火焰,推导了 DTF-FGM模型中特征标量(混合物分数和反应进度变量)及相应亚格子方差的大涡模拟输运方程。针对湍流分层火焰,由于采用copula方法考虑了混合物分数和反应进度变量之间的相关性,因此推导了 DTF-FGM模型中协方差的大涡模拟输运方程。作为不同亚格子模型的比较,建立了火焰面生成流形建表方法结合假定概率密度函数的亚格子模型(PPDF-FGM)。基于湍流预混火焰的计算结果,对DTF-FGM模型中重要参数, 如皱褶因子、加厚因子和亚格子方差模型等进行了敏感性分析。评估了 DTF-FGM和PPDF-FGM模型预测薄反应机制下湍流预混火焰和分层火焰结构的能力,然后采用当量比的概率密度分布,以及当量比和反应进度变量之间定向角的概率密度分布研究了湍流分层火焰结构。最后,基于详细化学建表结合假定概率密度函数的亚格子模型,对高温伴流湍流抬举火焰开展了大涡模拟研究。采用自点火模型耦合预混火焰传播模型构建详细化学热力学表,同时利用copula方法构建双特征标量的联合概率密度分布,然后推导了特征标量、亚格子方差以及协方差的大涡模拟输运方程。基于实验测量得到的散点分布和条件平均分布,对详细化学建表方法和联合概率密度函数模型进行了先验研究。通过湍流火焰传播速度简化公式,以及描述多机制火焰结构的多维火焰面方程初步研究了高温伴流湍流抬举火焰的驻定机制和燃烧机制。
[Abstract]:Low pollutant emission combustor design requirements promote the application of lean premixed combustion technology in gas turbines and aero-engines. Compared with non-premixed combustion, lean premixed combustion can reduce the peak temperature in the combustor and thus effectively reduce NO_x emissions. In the actual combustion chamber, space and time constraints affect fuel and oxygen. The degree of premixing between chemicals leads to the gradient of the equivalence ratio of premixed gases in space, which leads to stratified combustion. In order to effectively predict the complex flow structure, unsteady phenomena in combustion process and the complex interaction between turbulent vortex and flame, large eddy simulation method has been widely used. The difficulty lies in the coupling of nonlinear multi-scale turbulence and multi-scale chemical reactions, which makes it difficult to model and solve the source terms of chemical reactions.In this paper, several sub-lattice models are developed for turbulent premixing and stratified flame. The main work and innovations are as follows: Firstly, the large eddy simulation of the cold flow field in a Cambridge swirl burner is carried out. The statistical results of the large eddy simulation agree well with the experimental results, which verifies the accuracy of the numerical method. Based on the power spectral density, the vortex shedding and the oscillation of flow field caused by the existence of precession vortex core are analyzed. Secondly, based on the detailed chemical table and the sub-lattice model with assumed probability density function, the large eddy simulation of the high Karlovitz number on-duty premixed jet flame is carried out. The detailed chemical thermodynamic table is constructed by using the self-ignition model coupled with the premixed flame propagation model. The ability of the coupled tabulation method to predict the chemical thermodynamic state of a one-dimensional unsteady laminar premixed flame at the temperature of an unburned gas is evaluated. The interaction between turbulence and chemical reactions is considered using the assumed probability density function, in which the probability density distribution of the fraction of two mixtures is assumed to be Dirichlet distribution. The effects of different detailed chemical tabulating methods and different assumed probability density function models on the calculated results are analyzed, and then the flow field and flame structure of the high Karlovitz number on-duty premixed jet flame are analyzed. Furthermore, the thin reaction mechanism is studied based on the sublattice model (DTF-FGM) of the dynamic thickened flame combined with the flame surface generation manifold method. Large eddy simulation of turbulent premixed and stratified flames was carried out. The thickening factor was dynamically determined by the flame index defined by the reaction rate variable, so that the thickening process was limited to the area where the actual calculation needed to be thickened. Large eddy simulation transport equation with sublattice variance is derived for turbulent stratified flame. Considering the correlation between mixture fraction and reaction progress variables, the large eddy simulation transport equation with covariance in DTF-FGM model is derived. As a comparison of different sublattice models, the flame surface generation manifold table is established. Methods Based on the calculation results of turbulent premixed flame, the sensitivity analysis of important parameters in DTF-FGM model, such as wrinkle factor, thickening factor and sublattice variance model, was carried out by combining PPDF-FGM model with assumed probability density function. The ability of stratified flame structure is studied by using the probability density distribution of equivalent ratio and the probability density distribution of the directional angle between the equivalent ratio and the reaction progress variable. Large eddy simulation (LES). A detailed chemical thermodynamic table is constructed by coupling the self-ignition model with the premixed flame propagation model. The joint probability density distribution of the two characteristic scalars is constructed by using the copula method. Then the LES transport equations of the characteristic scalar, sublattice variance and covariance are derived. The detailed chemical tabulation method and the joint probability density function model are studied priorily. The stationary mechanism and combustion mechanism of high-temperature turbulent wake-lift flame are preliminarily studied by using the simplified formula of turbulent flame propagation velocity and the multi-dimensional flame surface equation describing the multi-mechanism flame structure.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK16
，
本文编号：2233632
[Abstract]:Low pollutant emission combustor design requirements promote the application of lean premixed combustion technology in gas turbines and aero-engines. Compared with non-premixed combustion, lean premixed combustion can reduce the peak temperature in the combustor and thus effectively reduce NO_x emissions. In the actual combustion chamber, space and time constraints affect fuel and oxygen. The degree of premixing between chemicals leads to the gradient of the equivalence ratio of premixed gases in space, which leads to stratified combustion. In order to effectively predict the complex flow structure, unsteady phenomena in combustion process and the complex interaction between turbulent vortex and flame, large eddy simulation method has been widely used. The difficulty lies in the coupling of nonlinear multi-scale turbulence and multi-scale chemical reactions, which makes it difficult to model and solve the source terms of chemical reactions.In this paper, several sub-lattice models are developed for turbulent premixing and stratified flame. The main work and innovations are as follows: Firstly, the large eddy simulation of the cold flow field in a Cambridge swirl burner is carried out. The statistical results of the large eddy simulation agree well with the experimental results, which verifies the accuracy of the numerical method. Based on the power spectral density, the vortex shedding and the oscillation of flow field caused by the existence of precession vortex core are analyzed. Secondly, based on the detailed chemical table and the sub-lattice model with assumed probability density function, the large eddy simulation of the high Karlovitz number on-duty premixed jet flame is carried out. The detailed chemical thermodynamic table is constructed by using the self-ignition model coupled with the premixed flame propagation model. The ability of the coupled tabulation method to predict the chemical thermodynamic state of a one-dimensional unsteady laminar premixed flame at the temperature of an unburned gas is evaluated. The interaction between turbulence and chemical reactions is considered using the assumed probability density function, in which the probability density distribution of the fraction of two mixtures is assumed to be Dirichlet distribution. The effects of different detailed chemical tabulating methods and different assumed probability density function models on the calculated results are analyzed, and then the flow field and flame structure of the high Karlovitz number on-duty premixed jet flame are analyzed. Furthermore, the thin reaction mechanism is studied based on the sublattice model (DTF-FGM) of the dynamic thickened flame combined with the flame surface generation manifold method. Large eddy simulation of turbulent premixed and stratified flames was carried out. The thickening factor was dynamically determined by the flame index defined by the reaction rate variable, so that the thickening process was limited to the area where the actual calculation needed to be thickened. Large eddy simulation transport equation with sublattice variance is derived for turbulent stratified flame. Considering the correlation between mixture fraction and reaction progress variables, the large eddy simulation transport equation with covariance in DTF-FGM model is derived. As a comparison of different sublattice models, the flame surface generation manifold table is established. Methods Based on the calculation results of turbulent premixed flame, the sensitivity analysis of important parameters in DTF-FGM model, such as wrinkle factor, thickening factor and sublattice variance model, was carried out by combining PPDF-FGM model with assumed probability density function. The ability of stratified flame structure is studied by using the probability density distribution of equivalent ratio and the probability density distribution of the directional angle between the equivalent ratio and the reaction progress variable. Large eddy simulation (LES). A detailed chemical thermodynamic table is constructed by coupling the self-ignition model with the premixed flame propagation model. The joint probability density distribution of the two characteristic scalars is constructed by using the copula method. Then the LES transport equations of the characteristic scalar, sublattice variance and covariance are derived. The detailed chemical tabulation method and the joint probability density function model are studied priorily. The stationary mechanism and combustion mechanism of high-temperature turbulent wake-lift flame are preliminarily studied by using the simplified formula of turbulent flame propagation velocity and the multi-dimensional flame surface equation describing the multi-mechanism flame structure.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK16
，
本文编号：2233632
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