湍流稀液霧兩相流燃燒的大渦模擬和火焰面模型相關(guān)問題研究
發(fā)布時(shí)間：2018-11-13 11:24
【摘要】：稀液霧燃燒工程應(yīng)用廣泛,深受研究者關(guān)注。隨著計(jì)算能力的增強(qiáng)和數(shù)值模型的不斷優(yōu)化,數(shù)值模擬在研究稀液霧燃燒機(jī)理、指導(dǎo)燃燒器設(shè)計(jì)等方面發(fā)揮著越來越重要的作用。大渦模擬(LES)方法能夠求解湍流中的大尺度含能結(jié)構(gòu),基于火焰面的模型能夠耦合詳細(xì)反應(yīng)機(jī)理并有很大潛力預(yù)測非穩(wěn)態(tài)過程,這兩種方法在稀液霧燃燒中的應(yīng)用勢在必然。然而把傳統(tǒng)氣相燃燒模型推廣到兩相流中需要對(duì)模型改進(jìn)以考慮更多的物理過程。改進(jìn)相關(guān)模型并研究其應(yīng)用范圍、探究模型的理論基礎(chǔ)和分析流場中氣液相互作用等是相關(guān)工作的熱點(diǎn)�；诖�,本文對(duì)火焰面模型在稀液霧燃燒中的應(yīng)用進(jìn)行了相關(guān)研究,主要工作如下： 首先,基于非預(yù)混的火焰面模型和LES方法對(duì)CH4/H2/N2湍流射流擴(kuò)散火焰進(jìn)行模擬,對(duì)比穩(wěn)態(tài)火焰面(SFM)模型和火焰面/進(jìn)度變量(FPV)模型在氣相燃料燃燒中的性能。發(fā)現(xiàn)兩者都較好預(yù)測流場中一階矩和二階矩,而后者對(duì)二階矩的模擬更準(zhǔn)確。同時(shí)兩種模型對(duì)小濃度組分(小組分)的預(yù)測存在誤差。如果單獨(dú)求解小組分輸運(yùn)方程可較好解決這個(gè)問題。流場的本征正交分解(POD)分析發(fā)現(xiàn)前5階模態(tài)占有總湍流能量的60%左右,而中心射流區(qū)域集中著各尺度的湍流相干結(jié)構(gòu)。隨后通過對(duì)有回流區(qū)稀液霧受限射流、自由射流湍流流場的大渦模擬來研究流場中氣液相互作用。有回流區(qū)的稀液霧受限射流中發(fā)現(xiàn)Stokes數(shù)大的液滴彌散受其初始慣性影響較大,而Stokes數(shù)在1附近的小液滴分布在大渦結(jié)構(gòu)的外緣,彌散受氣相流場結(jié)構(gòu)的影響更大。冷態(tài)條件下,液霧單位體積蒸發(fā)速率和液霧彌散分布密切相關(guān),而單液滴蒸發(fā)速率受液滴滑移速度影響明顯。這兩方面的工作驗(yàn)證了FPV模型的有效性并分析了冷態(tài)條件下的液滴彌散和蒸發(fā)作用。 其次,對(duì)均勻各向同性湍流下正庚烷液滴自點(diǎn)火過程進(jìn)行直接數(shù)值模擬(DNS)研究,評(píng)估不同局部放熱指標(biāo)的性能,分析燃燒機(jī)制。DNS中采用詳細(xì)反應(yīng)機(jī)理并直接求解組分輸運(yùn)方程。通過對(duì)時(shí)間演化過程、瞬時(shí)圖、散點(diǎn)圖和擬合直線的分析發(fā)現(xiàn)[OH]×[CH2O]在自點(diǎn)火火焰中作為火焰放熱指標(biāo)是合適的。不同火焰機(jī)制時(shí)[OH]×[CH2O]和局部放熱速率基本滿足正比關(guān)系,但比例系數(shù)稍有變化。 再則,在歐拉-拉格朗日架構(gòu)下采用FPV模型和LES方法模擬了乙醇-空氣稀液霧駐定火焰,并提出在火焰面架構(gòu)中考慮蒸發(fā)吸熱效應(yīng)的修正模型。修正模型一種是基于修改層流火焰面,一種則側(cè)重在流體計(jì)算中考慮能量平衡。對(duì)修正模型的對(duì)比發(fā)現(xiàn),提出的降低火焰面溫度的N-FPV模型和在流場計(jì)算中考慮能量平衡的T-FPV模型都可以有效地模擬蒸發(fā)吸熱,同時(shí)看到模型對(duì)氣相和液相的統(tǒng)計(jì)參數(shù)具有很好的預(yù)測性能。瞬時(shí)圖分析發(fā)現(xiàn)在x/D=20上游FPV模型也能給出部分點(diǎn)火、熄火現(xiàn)象,而較強(qiáng)的蒸發(fā)作用發(fā)生在剪切層和x/D=20附近高溫區(qū)。數(shù)值結(jié)果表明,蒸發(fā)速率分布受液滴密度和氣相溫度的共同影響。 然后,采用LES方法耦合FPV模型對(duì)甲醇和正庚烷燃料高溫伴流中的自點(diǎn)火過程進(jìn)行了模擬,驗(yàn)證火焰面模型對(duì)自點(diǎn)火預(yù)測特性。為使FPV模型適用存在三個(gè)熱化學(xué)進(jìn)口狀態(tài)(液相燃料、載氣和高溫伴流)的燃燒系統(tǒng),本文引入新的守恒標(biāo)量對(duì)FPV模型進(jìn)行擴(kuò)展。數(shù)值結(jié)果表明,新提出的三進(jìn)口狀態(tài)模型的火焰瞬時(shí)圖像能合理地預(yù)測溫度和組分質(zhì)量分?jǐn)?shù)分布,尤其在噴嘴出口附近,較傳統(tǒng)雙進(jìn)口系統(tǒng)具有更好的預(yù)測特性。然而要有效地預(yù)測稀液霧燃燒中的點(diǎn)火過程需解決抬舉高度被高估的問題。隨后,本文采用自點(diǎn)火模型耦合新提出的三進(jìn)口狀態(tài)模型對(duì)稀液霧抬舉火焰進(jìn)行了模擬,得到的一系列火焰抬舉高度和統(tǒng)計(jì)量,與實(shí)驗(yàn)值符合良好,說明自點(diǎn)火模型適合這類火焰。對(duì)模擬結(jié)果分析可發(fā)現(xiàn),隨著液相燃料質(zhì)量流率的增加火焰抬舉高度下降,點(diǎn)火首先發(fā)生在貧燃、標(biāo)量耗散率小的位置。自由基OH往往出現(xiàn)在火焰生成點(diǎn)的上游。在火焰生成點(diǎn)上游,中心射流和高溫伴流的剪切層中存在少數(shù)小點(diǎn)火核心,是點(diǎn)火的預(yù)兆。 最后,針對(duì)反應(yīng)進(jìn)度參數(shù)的定義沒有考慮重油燃料的熱解等情況,提出反應(yīng)進(jìn)度參數(shù)的新定義。采用主成分分析(PCA)這一數(shù)學(xué)工具提出在基于火焰面的燃燒降維處理中優(yōu)化反應(yīng)進(jìn)度參數(shù)定義。對(duì)預(yù)混火焰面數(shù)據(jù)庫應(yīng)用PCA和核密度加權(quán)PCA (KEDPCA)并依據(jù)前兩個(gè)主元得到了優(yōu)化的反應(yīng)進(jìn)度參數(shù)定義。通過模擬/重構(gòu)一個(gè)CH4/N2/空氣抬舉火焰驗(yàn)證新定義的有效性。數(shù)值結(jié)果表明,新定義可以保證熱化學(xué)變量和反應(yīng)進(jìn)度參數(shù)之間的單調(diào)性。在層流抬舉火焰的模擬過程中發(fā)現(xiàn)優(yōu)化的反應(yīng)進(jìn)度參數(shù)比傳統(tǒng)的定義有更好的表現(xiàn)。溫度和OH質(zhì)量分?jǐn)?shù)的云圖說明基于PCA的優(yōu)化定義在高溫區(qū)表現(xiàn)得更好。R2統(tǒng)計(jì)系數(shù)說明除部分小組分外,KEDPCA結(jié)果比PCA稍好但差距不明顯。KEDPCA方法的最主要優(yōu)勢體現(xiàn)在它受原始數(shù)據(jù)庫中插值等操作的影響很小,PCA則對(duì)原始數(shù)據(jù)庫中的狀態(tài)變化更敏感。通過研究,本文給出反應(yīng)進(jìn)度參數(shù)或降維參數(shù)定義的普遍準(zhǔn)則。
[Abstract]:The application of the thin-liquid fog combustion engineering is widely used, and it is deeply concerned by the researchers. With the enhancement of the computing power and the continuous optimization of the numerical model, the numerical simulation plays a more and more important role in the research of the mechanism of the lean liquid fog and the design of the burner. The large eddy simulation (LES) method can solve the large-scale energy-bearing structure in the turbulent flow, and the model of the flame surface can be coupled with the detailed reaction mechanism and has a great potential to predict the unsteady process. however, that extension of the conventional gas-phase combustion model to the two-phase flow requires the improvement of the model to take into account more physical processes. To improve the relevant model and to study the application range of the model, the theoretical basis of the model and the interaction of the gas and liquid in the flow field are the hot points of the related work. Based on this, the application of the flame surface model in the lean liquid fog combustion is studied. The main work is as follows: First, the diffusion flame of CH4/ H2/ N2 turbulent jet is carried out based on the non-premixed flame surface model and the LES method Simulation, comparison of steady-state flame surface (SFM) model and flame surface/ progress variable (FPV) model in gas-phase fuel combustion It is found that both the first and second moments in the flow field are better predicted, and the latter is more suitable for the simulation of second-order moments. Accurate. The prediction of the small-concentration component (group) by the two models Error. If a separate solution is used to solve the sub-transport equation, this problem can be solved well The orthogonal decomposition (POD) analysis of the flow field shows that the first 5-step mode occupies about 60% of the total turbulent energy, while the central jet region is concentrated on the turbulence coherence of each scale. in that flow field, the gas-liquid in the flow field is study by the large-eddy simulation of the turbulent flow field of the free-jet turbulent flow through the dilute-liquid-fog-restricted jet with the return region, The small droplets in the vicinity of the Stokes number are distributed in the outer edge of the large-vortex structure and the dispersion is influenced by the structure of the gas-phase flow field. Under the condition of cold state, the volume evaporation rate of the liquid fog unit is closely related to the dispersion distribution of the liquid fog, and the evaporation rate of the single liquid drop is affected by the speed of the liquid drop sliding speed. It is clear that the effectiveness of the FPV model is verified and the dispersion and evaporation of the droplets in the cold state are analyzed. in that follow, the direct numerical simulation (DNS) study on the self-ignition of the n-heptane liquid drop under the homogeneous isotropic turbulence is carried out, and the performance of different local heat release indexes is evaluated. Analysis of combustion mechanism. The detailed reaction mechanism is used in DNS and the group is solved directly. By analyzing the time evolution process, the instantaneous diagram, the scatter diagram and the fitted straight line, the[OH]-[CH2O] is used as the flame heat-releasing finger in the self-ignition flame. The scale is suitable.[OH][CH2O] and the local heat release rate at different flame mechanisms basically satisfy the proportional relationship, but the scale system In the Euler-Lagrange architecture, the FPV model and LES method are used to simulate the flame of the ethanol-air thin liquid fog, and the evaporation and suction are considered in the flame surface structure. The modified model of the thermal effect. The modified model is based on the modified laminar flame, one on the fluid meter. The energy balance is considered in the calculation. The comparison of the modified model shows that the N-FPV model for reducing the temperature of the flame surface and the T-FPV model considering the energy balance in the flow field calculation can effectively simulate the evaporation and heat absorption, and the statistical parameters of the model to the gas phase and the liquid phase are also observed. The instantaneous graph analysis shows that the FPV model in the x/ D = 20 can also give partial ignition and flame-out, and the stronger evaporation takes place in the shear layer and the x/ D. = 20 high temperature area. Numerical results show that the evaporation rate distribution is affected by droplet density and gas The self-ignition process of methanol and n-heptane fuel high-temperature co-flow is simulated and the flame is verified by using LES method to couple the FPV model. In order to make the FPV model applicable to the combustion system of three thermochemical import states (liquid fuel, carrier gas and high temperature with flow), a new conservation standard is introduced in this paper. The numerical results show that the flame transient image of the newly proposed three-inlet state model can reasonably predict the distribution of temperature and component mass fraction, especially near the outlet of the nozzle. The system has better prediction characteristics. However, it is necessary to effectively predict the need of the ignition process in the lean-liquid-fog combustion. In this paper, a new three-inlet state model is used to simulate the high-lift flame of the thin-liquid fog, and a series of flame lifting heights and statistics are obtained, which are in good agreement with the experimental values. The self-ignition model is suitable for this kind of flame. The analysis of the simulation results shows that, with the increase of the mass flow rate of the liquid fuel, the lifting height of the flame is decreased, and the ignition first occurs in the lean state. the position where the rate of the scalar dissipation is small. the free radical OH tends to occurs upstream of the flame generation point. A small number of small shear layers upstream of the flame generation point, the central jet, and the high temperature tracing flow The ignition core is an omen of ignition. Finally, the definition of the reaction progress parameter does not take into account the conditions of the pyrolysis of the heavy oil fuel In this paper, a new definition of the reaction progress parameter is put forward. The main component analysis (PCA) is used to put forward the combustion drop based on the flame surface. The definition of the optimization reaction progress parameter in the dimensional process is defined. The PCA and the kernel density weighted PCA (KEDPCA) are applied to the pre-mixed flame surface database and the two main elements are based on the first two main elements. The optimized reaction progress parameter is defined. A CH4/ N2/ air is simulated/ reconstructed The effectiveness of the new definition of the gas lifting flame verification. The numerical results show that the new definition can ensure the thermochemical change Monotonicity between the amount and the reaction progress parameter. The optimized reaction progress was found during the simulation of the laminar flow-up flame. The parameter is better than the traditional definition. The image of the temperature and OH mass fraction is based on the PCA The optimization definition is better in the high temperature area. The R2 statistics show that, in addition to the partial group, the KEDPCA The result is better than PCA but the difference is not obvious. The most important advantage of the KEDPCA method is that it is affected by the interpolation and other operations in the original database. The state changes in the original database are more sensitive. By studying, this paper gives the progress of the reaction
【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】：2015
【分類號(hào)】：TK16
本文編號(hào)：2328968
[Abstract]:The application of the thin-liquid fog combustion engineering is widely used, and it is deeply concerned by the researchers. With the enhancement of the computing power and the continuous optimization of the numerical model, the numerical simulation plays a more and more important role in the research of the mechanism of the lean liquid fog and the design of the burner. The large eddy simulation (LES) method can solve the large-scale energy-bearing structure in the turbulent flow, and the model of the flame surface can be coupled with the detailed reaction mechanism and has a great potential to predict the unsteady process. however, that extension of the conventional gas-phase combustion model to the two-phase flow requires the improvement of the model to take into account more physical processes. To improve the relevant model and to study the application range of the model, the theoretical basis of the model and the interaction of the gas and liquid in the flow field are the hot points of the related work. Based on this, the application of the flame surface model in the lean liquid fog combustion is studied. The main work is as follows: First, the diffusion flame of CH4/ H2/ N2 turbulent jet is carried out based on the non-premixed flame surface model and the LES method Simulation, comparison of steady-state flame surface (SFM) model and flame surface/ progress variable (FPV) model in gas-phase fuel combustion It is found that both the first and second moments in the flow field are better predicted, and the latter is more suitable for the simulation of second-order moments. Accurate. The prediction of the small-concentration component (group) by the two models Error. If a separate solution is used to solve the sub-transport equation, this problem can be solved well The orthogonal decomposition (POD) analysis of the flow field shows that the first 5-step mode occupies about 60% of the total turbulent energy, while the central jet region is concentrated on the turbulence coherence of each scale. in that flow field, the gas-liquid in the flow field is study by the large-eddy simulation of the turbulent flow field of the free-jet turbulent flow through the dilute-liquid-fog-restricted jet with the return region, The small droplets in the vicinity of the Stokes number are distributed in the outer edge of the large-vortex structure and the dispersion is influenced by the structure of the gas-phase flow field. Under the condition of cold state, the volume evaporation rate of the liquid fog unit is closely related to the dispersion distribution of the liquid fog, and the evaporation rate of the single liquid drop is affected by the speed of the liquid drop sliding speed. It is clear that the effectiveness of the FPV model is verified and the dispersion and evaporation of the droplets in the cold state are analyzed. in that follow, the direct numerical simulation (DNS) study on the self-ignition of the n-heptane liquid drop under the homogeneous isotropic turbulence is carried out, and the performance of different local heat release indexes is evaluated. Analysis of combustion mechanism. The detailed reaction mechanism is used in DNS and the group is solved directly. By analyzing the time evolution process, the instantaneous diagram, the scatter diagram and the fitted straight line, the[OH]-[CH2O] is used as the flame heat-releasing finger in the self-ignition flame. The scale is suitable.[OH][CH2O] and the local heat release rate at different flame mechanisms basically satisfy the proportional relationship, but the scale system In the Euler-Lagrange architecture, the FPV model and LES method are used to simulate the flame of the ethanol-air thin liquid fog, and the evaporation and suction are considered in the flame surface structure. The modified model of the thermal effect. The modified model is based on the modified laminar flame, one on the fluid meter. The energy balance is considered in the calculation. The comparison of the modified model shows that the N-FPV model for reducing the temperature of the flame surface and the T-FPV model considering the energy balance in the flow field calculation can effectively simulate the evaporation and heat absorption, and the statistical parameters of the model to the gas phase and the liquid phase are also observed. The instantaneous graph analysis shows that the FPV model in the x/ D = 20 can also give partial ignition and flame-out, and the stronger evaporation takes place in the shear layer and the x/ D. = 20 high temperature area. Numerical results show that the evaporation rate distribution is affected by droplet density and gas The self-ignition process of methanol and n-heptane fuel high-temperature co-flow is simulated and the flame is verified by using LES method to couple the FPV model. In order to make the FPV model applicable to the combustion system of three thermochemical import states (liquid fuel, carrier gas and high temperature with flow), a new conservation standard is introduced in this paper. The numerical results show that the flame transient image of the newly proposed three-inlet state model can reasonably predict the distribution of temperature and component mass fraction, especially near the outlet of the nozzle. The system has better prediction characteristics. However, it is necessary to effectively predict the need of the ignition process in the lean-liquid-fog combustion. In this paper, a new three-inlet state model is used to simulate the high-lift flame of the thin-liquid fog, and a series of flame lifting heights and statistics are obtained, which are in good agreement with the experimental values. The self-ignition model is suitable for this kind of flame. The analysis of the simulation results shows that, with the increase of the mass flow rate of the liquid fuel, the lifting height of the flame is decreased, and the ignition first occurs in the lean state. the position where the rate of the scalar dissipation is small. the free radical OH tends to occurs upstream of the flame generation point. A small number of small shear layers upstream of the flame generation point, the central jet, and the high temperature tracing flow The ignition core is an omen of ignition. Finally, the definition of the reaction progress parameter does not take into account the conditions of the pyrolysis of the heavy oil fuel In this paper, a new definition of the reaction progress parameter is put forward. The main component analysis (PCA) is used to put forward the combustion drop based on the flame surface. The definition of the optimization reaction progress parameter in the dimensional process is defined. The PCA and the kernel density weighted PCA (KEDPCA) are applied to the pre-mixed flame surface database and the two main elements are based on the first two main elements. The optimized reaction progress parameter is defined. A CH4/ N2/ air is simulated/ reconstructed The effectiveness of the new definition of the gas lifting flame verification. The numerical results show that the new definition can ensure the thermochemical change Monotonicity between the amount and the reaction progress parameter. The optimized reaction progress was found during the simulation of the laminar flow-up flame. The parameter is better than the traditional definition. The image of the temperature and OH mass fraction is based on the PCA The optimization definition is better in the high temperature area. The R2 statistics show that, in addition to the partial group, the KEDPCA The result is better than PCA but the difference is not obvious. The most important advantage of the KEDPCA method is that it is affected by the interpolation and other operations in the original database. The state changes in the original database are more sensitive. By studying, this paper gives the progress of the reaction
【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】：2015
【分類號(hào)】：TK16
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