湍流預混和分層燃燒中亞格子模型研究及其在大渦模擬中的應用
發(fā)布時間：2018-09-10 06:19
【摘要】：低污染物排放的燃燒室設計要求促進了貧燃預混燃燒技術在燃氣輪機和航空發(fā)動機中的應用。與非預混燃燒相比,貧燃預混燃燒能夠降低燃燒室內(nèi)峰值溫度,進而有效降低NO_x排放。在實際燃燒室內(nèi),空間和時間的約束影響了燃料和氧化劑之間的預混程度,導致預混氣體的當量比在空間呈現(xiàn)梯度,進而出現(xiàn)分層燃燒。為了有效預測復雜流場結(jié)構、燃燒過程中非定�，F(xiàn)象以及湍流渦旋與火焰復雜的相互作用,大渦模擬方法得到了廣泛應用。湍流燃燒大渦模擬的主要困難在于非線性的多尺度湍流和多尺度化學反應的相互耦合,導致化學反應源項模化及方程求解難度很大。本文緊緊圍繞湍流預混和分層火焰,發(fā)展了若干亞格子模型,并針對不同流場工況、不同駐定機制以及不同燃燒機制的若干典型湍流燃燒算例開展了大渦模擬研究。主要工作及創(chuàng)新點如下:首先,對劍橋旋流燃燒器的冷態(tài)流場進行了大渦模擬研究。大渦模擬統(tǒng)計結(jié)果與實驗結(jié)果符合較好,驗證了數(shù)值方法的準確性。在燃燒器出口的剪切層附近,采用Q準則識別了無旋流工況的環(huán)狀渦結(jié)構和有旋流工況的螺旋渦結(jié)構�；诠β首V密度分析了渦旋脫落的發(fā)生,以及進動渦核的存在導致流場的振蕩現(xiàn)象。采用三維本征正交分解提取了有旋流動中大尺度結(jié)構,預測了多種流動不穩(wěn)定現(xiàn)象,包括渦旋脫落、進動渦核和鈍體回流區(qū)末端的不穩(wěn)定性。其次,基于詳細化學建表結(jié)合假定概率密度函數(shù)的亞格子模型,對高Karlovitz數(shù)的值班預混射流火焰開展了大渦模擬研究。采用自點火模型耦合預混火焰?zhèn)鞑ツＰ蜆嫿ㄔ敿毣瘜W熱力學表。計算了不同未燃氣體溫度條件下一維非穩(wěn)態(tài)的層流預混火焰,對耦合建表方法預測化學熱力學狀態(tài)的能力進行了評估。使用假定概率密度函數(shù)考慮湍流和化學反應之間的相互作用,其中假定雙混合物分數(shù)的概率密度分布為Dirichlet分布。探討了不同詳細化學建表方法和不同假定概率密度函數(shù)模型對計算結(jié)果的影響,然后分析了高Karlovitz數(shù)的值班預混射流火焰的流場結(jié)構和火焰結(jié)構。再者,基于動態(tài)加厚火焰結(jié)合火焰面生成流形建表方法的亞格子模型(DTF-FGM),對薄反應機制下湍流預混和分層火焰開展了大渦模擬研究。利用反應進度變量定義的火焰指數(shù)動態(tài)確定加厚因子,使得加厚過程限制在實際計算需要加厚的區(qū)域。針對湍流預混火焰,推導了 DTF-FGM模型中特征標量(混合物分數(shù)和反應進度變量)及相應亞格子方差的大渦模擬輸運方程。針對湍流分層火焰,由于采用copula方法考慮了混合物分數(shù)和反應進度變量之間的相關性,因此推導了 DTF-FGM模型中協(xié)方差的大渦模擬輸運方程。作為不同亞格子模型的比較,建立了火焰面生成流形建表方法結(jié)合假定概率密度函數(shù)的亞格子模型(PPDF-FGM)�；谕牧黝A混火焰的計算結(jié)果,對DTF-FGM模型中重要參數(shù), 如皺褶因子、加厚因子和亞格子方差模型等進行了敏感性分析。評估了 DTF-FGM和PPDF-FGM模型預測薄反應機制下湍流預混火焰和分層火焰結(jié)構的能力,然后采用當量比的概率密度分布,以及當量比和反應進度變量之間定向角的概率密度分布研究了湍流分層火焰結(jié)構。最后,基于詳細化學建表結(jié)合假定概率密度函數(shù)的亞格子模型,對高溫伴流湍流抬舉火焰開展了大渦模擬研究。采用自點火模型耦合預混火焰?zhèn)鞑ツＰ蜆嫿ㄔ敿毣瘜W熱力學表,同時利用copula方法構建雙特征標量的聯(lián)合概率密度分布,然后推導了特征標量、亞格子方差以及協(xié)方差的大渦模擬輸運方程�；趯嶒灉y量得到的散點分布和條件平均分布,對詳細化學建表方法和聯(lián)合概率密度函數(shù)模型進行了先驗研究。通過湍流火焰?zhèn)鞑ニ俣群喕?以及描述多機制火焰結(jié)構的多維火焰面方程初步研究了高溫伴流湍流抬舉火焰的駐定機制和燃燒機制。
[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.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TK16
，
本文編號：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.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TK16
，
本文編號：2233632
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