湍流預(yù)混和分層燃燒中亞格子模型研究及其在大渦模擬中的應(yīng)用
發(fā)布時(shí)間：2018-09-10 06:19
【摘要】：低污染物排放的燃燒室設(shè)計(jì)要求促進(jìn)了貧燃預(yù)混燃燒技術(shù)在燃?xì)廨啓C(jī)和航空發(fā)動(dòng)機(jī)中的應(yīng)用。與非預(yù)混燃燒相比,貧燃預(yù)混燃燒能夠降低燃燒室內(nèi)峰值溫度,進(jìn)而有效降低NO_x排放。在實(shí)際燃燒室內(nèi),空間和時(shí)間的約束影響了燃料和氧化劑之間的預(yù)混程度,導(dǎo)致預(yù)混氣體的當(dāng)量比在空間呈現(xiàn)梯度,進(jìn)而出現(xiàn)分層燃燒。為了有效預(yù)測(cè)復(fù)雜流場(chǎng)結(jié)構(gòu)、燃燒過程中非定�，F(xiàn)象以及湍流渦旋與火焰復(fù)雜的相互作用,大渦模擬方法得到了廣泛應(yīng)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(xué)反應(yīng)的相互耦合,導(dǎo)致化學(xué)反應(yīng)源項(xiàng)�；胺匠糖蠼怆y度很大。本文緊緊圍繞湍流預(yù)混和分層火焰,發(fā)展了若干亞格子模型,并針對(duì)不同流場(chǎng)工況、不同駐定機(jī)制以及不同燃燒機(jī)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(diǎn)如下:首先,對(duì)劍橋旋流燃燒器的冷態(tài)流場(chǎng)進(jìn)行了大渦模擬研究。大渦模擬統(tǒng)計(jì)結(jié)果與實(shí)驗(yàn)結(jié)果符合較好,驗(yàn)證了數(shù)值方法的準(zhǔn)確性。在燃燒器出口的剪切層附近,采用Q準(zhǔn)則識(shí)別了無旋流工況的環(huán)狀渦結(jié)構(gòu)和有旋流工況的螺旋渦結(jié)構(gòu)�；诠β首V密度分析了渦旋脫落的發(fā)生,以及進(jìn)動(dòng)渦核的存在導(dǎo)致流場(chǎng)的振蕩現(xiàn)象。采用三維本征正交分解提取了有旋流動(dòng)中大尺度結(jié)構(gòu),預(yù)測(cè)了多種流動(dòng)不穩(wěn)定現(xiàn)象,包括渦旋脫落、進(jìn)動(dòng)渦核和鈍體回流區(qū)末端的不穩(wěn)定性。其次,基于詳細(xì)化學(xué)建表結(jié)合假定概率密度函數(shù)的亞格子模型,對(duì)高Karlovitz數(shù)的值班預(yù)混射流火焰開展了大渦模擬研究。采用自點(diǎn)火模型耦合預(yù)混火焰?zhèn)鞑ツＰ蜆?gòu)建詳細(xì)化學(xué)熱力學(xué)表。計(jì)算了不同未燃?xì)怏w溫度條件下一維非穩(wěn)態(tài)的層流預(yù)混火焰,對(duì)耦合建表方法預(yù)測(cè)化學(xué)熱力學(xué)狀態(tài)的能力進(jìn)行了評(píng)估。使用假定概率密度函數(shù)考慮湍流和化學(xué)反應(yīng)之間的相互作用,其中假定雙混合物分?jǐn)?shù)的概率密度分布為Dirichlet分布。探討了不同詳細(xì)化學(xué)建表方法和不同假定概率密度函數(shù)模型對(duì)計(jì)算結(jié)果的影響,然后分析了高Karlovitz數(shù)的值班預(yù)混射流火焰的流場(chǎng)結(jié)構(gòu)和火焰結(jié)構(gòu)。再者,基于動(dòng)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(duì)薄反應(yīng)機(jī)制下湍流預(yù)混和分層火焰開展了大渦模擬研究。利用反應(yīng)進(jìn)度變量定義的火焰指數(shù)動(dòng)態(tài)確定加厚因子,使得加厚過程限制在實(shí)際計(jì)算需要加厚的區(qū)域。針對(duì)湍流預(yù)混火焰,推導(dǎo)了 DTF-FGM模型中特征標(biāo)量(混合物分?jǐn)?shù)和反應(yīng)進(jìn)度變量)及相應(yīng)亞格子方差的大渦模擬輸運(yùn)方程。針對(duì)湍流分層火焰,由于采用copula方法考慮了混合物分?jǐn)?shù)和反應(yīng)進(jìn)度變量之間的相關(guān)性,因此推導(dǎo)了 DTF-FGM模型中協(xié)方差的大渦模擬輸運(yùn)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(yù)混火焰的計(jì)算結(jié)果,對(duì)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(jìn)行了敏感性分析。評(píng)估了 DTF-FGM和PPDF-FGM模型預(yù)測(cè)薄反應(yīng)機(jī)制下湍流預(yù)混火焰和分層火焰結(jié)構(gòu)的能力,然后采用當(dāng)量比的概率密度分布,以及當(dāng)量比和反應(yīng)進(jìn)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(gòu)。最后,基于詳細(xì)化學(xué)建表結(jié)合假定概率密度函數(shù)的亞格子模型,對(duì)高溫伴流湍流抬舉火焰開展了大渦模擬研究。采用自點(diǎn)火模型耦合預(yù)混火焰?zhèn)鞑ツＰ蜆?gòu)建詳細(xì)化學(xué)熱力學(xué)表,同時(shí)利用copula方法構(gòu)建雙特征標(biāo)量的聯(lián)合概率密度分布,然后推導(dǎo)了特征標(biāo)量、亞格子方差以及協(xié)方差的大渦模擬輸運(yùn)方程�；趯�(shí)驗(yàn)測(cè)量得到的散點(diǎn)分布和條件平均分布,對(duì)詳細(xì)化學(xué)建表方法和聯(lián)合概率密度函數(shù)模型進(jìn)行了先驗(yàn)研究。通過湍流火焰?zhèn)鞑ニ俣群?jiǎn)化公式,以及描述多機(jī)制火焰結(jié)構(gòu)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(jī)制和燃燒機(jī)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(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TK16
，
本文編號(hào)：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(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TK16
，
本文編號(hào)：2233632
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