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Distributed transfer function approach for one-dimensional thermoacoustic combustor models 一维热声燃烧室模型的分布传递函数方法
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-12-14 DOI: 10.1080/13647830.2022.2156930
M. Yoon
This paper proposes a new approach for one-dimensional thermoacoustic combustor models. Our new model is a transfer function estimated from the frequency response of the linearised Euler equation to a spatially normalised and temporally impulsive input. The proposed approach can deal with combustors with varying cross-sectional areas under a non-zero mean flow, distributed heating/cooling, and outlet boundary conditions involving entropy waves, overcoming limitations of the popular network model. In addition our new approach can provide a more reliable thermoacoustic model for combustors with entropy-related boundary conditions, remedying the inaccurate entropy model of the network model. Numerical comparisons of our new model with a network model show apparent similarities between the two, validating the new model. It is also observed that, compared to our new model, the network model is more sensitive to mean flow and significantly overestimates the entropy wave effects on combustor acoustics.
本文提出了一种一维热声燃烧室模型的新方法。我们的新模型是从线性化欧拉方程的频率响应估计到空间归一化和时间脉冲输入的传递函数。所提出的方法可以在非零平均流量、分布式加热/冷却和涉及熵波的出口边界条件下处理具有不同横截面积的燃烧器,克服了流行网络模型的局限性。此外,我们的新方法可以为具有熵相关边界条件的燃烧器提供一个更可靠的热声模型,纠正了网络模型中不准确的熵模型。我们的新模型与网络模型的数值比较表明,两者之间有明显的相似性,验证了新模型。还观察到,与我们的新模型相比,网络模型对平均流量更敏感,并且显著高估了熵波对燃烧器声学的影响。
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引用次数: 0
An improved stiff-ODE solving framework for reacting flow simulations with detailed chemistry in OpenFOAM 用于OpenFOAM中具有详细化学的反应流模拟的改进的刚性ODE求解框架
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-12-12 DOI: 10.1080/13647830.2022.2153739
Kun Wu, Yuting Jiang, Zhijie Huo, D. Cheng, Xuejun Fan
The integration of stiff ordinary differential equation (ODE) systems associated with detailed chemical kinetics is computationally demanding in practical combustion simulations. Despite the various approaches in expediting the computational efficiency, it is still necessary to optimise the cell-wise calculation in operator-splitting type simulations of reactive flow. In this work, we proposed an improved stiff-ODE solver framework targeting to speed up the simulation of reactive flow in OpenFOAM. This framework combines the Radau-IIA and backward differentiation formula (BDF) ODE-integration algorithms, the pyJac-based fully analytical Jacobian formulation, and dense-based LAPACK and sparse-based KLU sophisticated linear system solvers. We evaluate the performance of the efficient solver framework on various benchmark combustion problems across a wide range of chemical kinetic complexities. A comprehensive investigation of the key elements of stiff ODE solvers is conducted in the homogeneous reactor, focusing respectively on the influences of error tolerance, integration time interval, Jacobian evaluation methodology, and linear system solver on the accuracy and efficiency trade-off. More realistic simulation results are presented regarding the one-dimensional laminar flame and three-dimensional turbulent flame. The results indicate that the Radau-IIA is more preferable in both efficiency and accuracy compared with the widely used BDF and Seulex methods for large integration interval, whereas the differences between three methods diminish as the integration time interval decreases. In all cases, it is found that the full analytical Jacobian is more advantageous for small mechanisms of species number around 50–100 while the approximated formulation of Jacobian is recommended for larger ones. Furthermore, the more robust linear system solvers provide significant improvement on computational efficiency with the dense-based LAPACK solver being more suitable for small to moderate-scale mechanisms while sparse-based KLU being superior for large-scale mechanisms. The proposed efficient solver framework in its optimal configuration obtains more than 2.6 times speedup in realistic high-fidelity flame simulation with a 57 species combustion mechanism.
在实际的燃烧模拟中,与详细化学动力学相关的刚性常微分方程(ODE)系统的积分计算要求很高。尽管有各种方法可以提高计算效率,但在算子分裂型反应流模拟中,仍有必要对基于单元的计算进行优化。在这项工作中,我们提出了一个改进的刚性ode求解器框架,旨在加快OpenFOAM中反应流的模拟。该框架结合了Radau-IIA和后向微分公式(BDF) ode集成算法,基于pyjack的全解析雅可比公式,以及基于密度的LAPACK和基于稀疏的KLU复杂线性系统求解器。我们评估了高效求解器框架在各种基准燃烧问题上的性能,这些问题涉及广泛的化学动力学复杂性。在均匀反应器中,对刚性ODE求解器的关键要素进行了全面的研究,分别关注了误差容限、积分时间间隔、雅可比评估方法和线性系统求解器对精度和效率权衡的影响。给出了一维层流火焰和三维湍流火焰较为真实的模拟结果。结果表明,在大积分区间下,Radau-IIA方法在效率和精度上均优于目前广泛使用的BDF和Seulex方法,且随着积分时间区间的减小,三种方法之间的差异逐渐减小。在所有情况下,发现对于种数在50-100左右的小型机构,全解析雅可比矩阵更有利,而对于较大的机构,建议使用近似雅可比矩阵。此外,鲁棒性更好的线性系统求解器显著提高了计算效率,其中基于密度的LAPACK求解器更适合中小型机构,而基于稀疏的KLU求解器更适合大型机构。在57种燃烧机制的真实高保真火焰模拟中,所提出的高效求解器框架在其最优配置下获得了2.6倍以上的加速。
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引用次数: 0
Comparison of combustion duration and end-gas autoignition in inwardly and outwardly propagating flames induced by different ignition configurations 不同点火方式引起的向内和向外蔓延火焰的燃烧持续时间和末端气体自燃比较
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-12-09 DOI: 10.1080/13647830.2022.2153741
Linlin Yang, Yiqing Wang, Zheng Chen
Recently, multiple spark ignition has received great attention since it helps to increase thermal efficiency and to reduce misfire in engines. Multiple spark ignition also affects the combustion duration and thereby it can be used for knock control. However, previous studies reported opposite trends in terms of how multiple spark ignition affects engine knock. This work aims to assess and interpret the influence of flame propagation direction induced by different ignition configurations on combustion duration and end-gas autoignition/engine knock. Two simplified and idealised ignition configurations are studied theoretically and numerically. One is with infinite number of sparks at side circular wall, which induces an inwardly propagating flame (IPF); and the other is with a single central spark, which induces an outwardly propagating flame (OPF). In the asymptotic theoretical analysis, the canonical 1D formulations for IPF and OPF are reduced to 0D model. Based on the 0D model, OPF and IPF at different initial temperatures are studied and compared. Counterintuitively, it is found that the combustion duration of OPF is shorter than that of IPF when there is no end-gas autoignition. On the other hand, the combustion duration of IPF is shorter than that of OPF when end-gas autoignition occurs. Furthermore, end-gas autoignition is found to be more prone to occur in IPF than OPF. These interesting observations are interpreted through assessing the ignition delay time and different components of the absolute flame propagation speed. The theoretical results are validated by transient simulations considering detailed chemistry and transport which are conducted for IPF and OPF in an iso-octane/air mixture at different initial temperatures and pressures. Both theoretical and numerical results suggest that compared to infinite number of ignition sparks at side wall, the single central ignition has the advantages in shortening the combustion duration and reducing the tendency of end-gas autoignition.
近年来,多火花点火由于有助于提高发动机的热效率和减少失火而受到极大的关注。多火花点火也会影响燃烧持续时间,因此可以用于爆震控制。然而,先前的研究报告了多火花点火如何影响发动机爆震的相反趋势。本工作旨在评估和解释不同点火配置引起的火焰传播方向对燃烧持续时间和尾气自燃/发动机爆震的影响。对两种简化和理想化的点火结构进行了理论和数值研究。一种是在侧圆壁处产生无限数量的火花,产生向内传播的火焰(IPF);另一种是具有单个中心火花,该中心火花引起向外传播的火焰(OPF)。在渐近理论分析中,将IPF和OPF的规范1D公式简化为0D模型。基于0D模型,对不同初始温度下的OPF和IPF进行了研究和比较。与直觉相反,在没有末端气体自燃的情况下,OPF的燃烧持续时间比IPF短。另一方面,当发生末端气体自燃时,IPF的燃烧持续时间短于OPF。此外,IPF比OPF更容易发生末端气体自燃。这些有趣的观察结果是通过评估点火延迟时间和绝对火焰传播速度的不同分量来解释的。通过瞬态模拟验证了理论结果,该模拟考虑了不同初始温度和压力下异辛烷/空气混合物中IPF和OPF的详细化学和传输。理论和数值计算结果表明,与侧壁无限数量的点火火花相比,单中心点火具有缩短燃烧时间和减少末端气体自燃倾向的优点。
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引用次数: 0
Experimental study and thermodynamic analysis of coal spontaneous combustion characteristics 煤自燃特性的实验研究与热力学分析
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-12-09 DOI: 10.1080/13647830.2022.2153742
Minbo Zhang, Zichao Wang, Longkang Wang, Zhen Zhang, Dangyu Zhang, Chunxin Li
Spontaneous coal combustion is one of the most common disasters in coal mine production. In order to explore the mechanism of coal spontaneous combustion more deeply, coal samples from the Yangdong wellfield of Jizhong Energy were selected for oxidative heat energy analysis experiments. A temperature-programmed experiment was selected to study the changes in characteristic parameters during the low-temperature oxidation of coal under different air supply conditions. TG-DSC experiments were conducted to study the characteristic temperature changes and thermodynamic characteristics of coal combustion processes at different heating rates. The study results show that the coal is most easily oxidised in the low-temperature oxidation stage when the air supply is 120 ml/min. The oxygen consumption rate, CO generation rate, and maximum and minimum heat release intensity are all greater at this airflow than under other conditions. The process of spontaneous combustion of coal has six characteristic temperature points and is divided into five stages. The characteristic temperature of the coal sample increased with the increase of the heating rate, and the TG/DTG curve showed a hysteresis phenomenon. DSC temperature curve shifts toward the high temperature with the increase of the heating rate, and the exothermic region is expanded. Isokinetic analysis (F-W-O and V-W) and Coats-Redfern model for calculating thermodynamic parameters. The activation energy of the samples decreased with the increase of the heating rate in the range of 2∼20°C·min−1 and showed a decreasing trend with the increase of the conversion rate.
自燃是煤矿生产中最常见的灾害之一。为了更深入地探讨煤的自燃机理,选取冀中能源杨东井田煤样进行氧化热能分析实验。采用程序升温实验研究了不同供气条件下煤低温氧化过程中特征参数的变化。通过TG-DSC实验研究了不同升温速率下煤燃烧过程的特征温度变化和热力学特性。研究结果表明,当供气量为120时,煤在低温氧化阶段最容易被氧化 ml/分钟。在这种气流下,氧气消耗率、CO生成率以及最大和最小热释放强度都比在其他条件下更大。煤的自燃过程有六个特征温度点,分为五个阶段。煤样的特征温度随着加热速率的增加而增加,TG/DTG曲线呈现滞后现象。DSC温度曲线随着加热速率的增加而向高温方向移动,放热区域扩大。等速分析(F-W-O和V-W)和用于计算热力学参数的Coats-Redfern模型。在2~20°C·min−1的范围内,样品的活化能随着加热速率的增加而降低,并随着转化率的增加呈下降趋势。
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引用次数: 6
Application of machine learning in low-order manifold representation of chemistry in turbulent flames 机器学习在湍流火焰低阶流形化学表示中的应用
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-12-08 DOI: 10.1080/13647830.2022.2153740
Arash Mousemi, M. Jadidi, S. Dworkin, W. Bushe
The Uniform Conditional State (UCS) and the Multidimensional Flamelet Manifold (MFM) models are methods for the tabulation of chemistry in simulations of turbulent flames. The high-dimensionality of the tables these models generate and many possible combinations of the values for the input variables necessitate the allocation of a considerable size of memory during CFD calculations. This issue becomes even more problematic when adding more conditioning variables to the model. In this study, two Artificial Intelligence (AI)-based approaches referred to as Decision Tree (DT) and Artificial Neural Network (ANN) are developed and tested to provide in situ chemistry representation. The goal is to predict four parameters (outputs) accurately with low memory demand and computational cost. The trained AI models are then employed for simulation of a turbulent premixed flame. Comparison of the results from the AI-based approaches to those from the conventional UCS model shows acceptable agreement. The memory and CPU requirements from the different approaches are compared. It is found that the ANN model reduces the size of the chemistry table by around 92%. Conversely, the DT-based model reduces the size of the chemistry model by only 40%. The CPU time for using the DT model during the CFD calculations was around 10% shorter than the conventional approach while it was 8% higher for the ANN model. It was concluded that, based on the particular applications, different AI-based methods can facilitate an efficient representation of the chemistry manifold.
均匀条件态(UCS)和多维火焰流形(MFM)模型是湍流火焰模拟中的化学制表方法。这些模型生成的表格的高维性以及输入变量值的许多可能组合需要在CFD计算期间分配相当大的内存。当向模型中添加更多条件调节变量时,这个问题变得更加成问题。在本研究中,开发并测试了两种基于人工智能(AI)的方法,即决策树(DT)和人工神经网络(ANN),以提供原位化学表示。目标是在低内存需求和计算成本的情况下准确预测四个参数(输出)。然后将训练好的人工智能模型用于湍流预混火焰的模拟。将基于人工智能的方法与传统UCS模型的结果进行了比较,结果一致。比较了不同方法的内存和CPU需求。研究发现,人工神经网络模型将化学表的大小减少了92%左右。相反,基于dt的模型仅将化学模型的尺寸减小了40%。在CFD计算过程中,使用DT模型的CPU时间比传统方法缩短了10%左右,而使用ANN模型的CPU时间则提高了8%。结论是,基于特定的应用,不同的基于人工智能的方法可以促进化学歧管的有效表示。
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引用次数: 3
Optimisation method for automatic selection of rate constants of global reaction mechanisms 全局反应机理速率常数自动选择的优化方法
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-12-08 DOI: 10.1080/13647830.2022.2153743
Aleksander D. Zakharov, R. Fursenko, S. Minaev
Optimisation approach to automate selection of global reaction mechanisms rate constants is proposed and studied. The objective of optimisation is to find reaction rate constants minimising deviation of some flame characteristics (e.g. laminar burning velocity, ignition delay time, etc.) calculated by global mechanism from their reference values known from experiments or computed by detailed mechanisms. Examples of one, two and four step mechanisms optimisation with respect to laminar burning velocity and concentration distributions in counterflow diffusion flame are given. Computer codes implementing optimisation algorithm for these examples are also afforded and can be modified and used for reaction constants selection in various applications. Uniqueness of singlecriteria and multicriteria optimisation solutions is studied numerically by computations with different initial guesses and by direct evaluation of the objective functions. Particularly, it is found that for considered global mechanisms the minimum value of objective function is reached in some subdomain of the parametric space. This means that any values of rate parameters from this subdomain results in almost the same deviations of chosen flame characteristic from its reference value.
提出并研究了自动选择全局反应机理速率常数的优化方法。优化的目的是找到反应速率常数,使全局机制计算的某些火焰特性(如层流燃烧速度、点火延迟时间等)与实验已知或详细机制计算的参考值之间的偏差最小化。给出了关于逆流扩散火焰中层流燃烧速度和浓度分布的一步、二步和四步机构优化的例子。还提供了实现这些实例的优化算法的计算机代码,并且可以对其进行修改并用于各种应用中的反应常数选择。通过不同初始猜测的计算和目标函数的直接评估,对单准则和多准则优化解的唯一性进行了数值研究。特别地,我们发现对于所考虑的全局机制,在参数空间的一些子域中达到了目标函数的最小值。这意味着,来自该子域的任何速率参数值都会导致所选火焰特性与其参考值的偏差几乎相同。
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引用次数: 2
Effect of hydrogen addition on the consumption speed of lean premixed laminar methane flames exposed to combined strain and heat loss 氢气添加对贫预混层流甲烷火焰在应变和热损失联合作用下消耗速度的影响
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-11-28 DOI: 10.1080/13647830.2023.2182235
Alex M. Garcia, S. Le Bras, W. Polifke
This study presents a numerical analysis of the impact of hydrogen addition on the consumption speed of premixed lean methane-air laminar flames exposed to combined strain and heat loss. Equivalence ratios of 0.9, 0.7, and 0.5 with fuel mixture composition ranging from pure methane to pure hydrogen are considered to cover a wide range of conditions in the lean region. The 1-D asymmetric counter-flow premixed laminar flame (aCFPF) with heat loss on the product side is considered as a flamelet configuration that represents an elementary unit of a turbulent flame and the consumption speed is used to characterise the effect of strain and heat loss. Due to the ambiguity in the definition of the consumption speed of multi-component mixtures, two definitions are compared. The first definition is based on a weighted combination of the consumption rate of the fuel species and the second one is based in the global heat release rate. The definition of the consumption speed based on the heat release results in lower values of the stretched flame speed and even an opposite response to strain rate for some methane-hydrogen-air mixtures compared to the definition based on the fuel consumption. Strain rate leads to an increase of the flame speed for the lean methane-hydrogen mixtures, reaching a maximum value after which the flame speed decreases with strain rate. Heat loss decreases the stretched flame speed and leads to a sooner extinction of the flamelet due to combined strain and heat loss. Hydrogen addition and equivalence ratio significantly impact the maximum consumption speed and the flame response to combined strain rate and heat loss. The effect of hydrogen on the thermo-diffusive properties of the mixture, characterised by the Zeldovich number and the effective Lewis number, are also analyzed and related to the effect on the consumption speed. Two definitions of the Lewis number of the multi-component fuel mixture are evaluated against the results from the aCFPF.
本研究对氢气添加对暴露于应变和热损失组合下的预混贫甲烷-空气层流火焰消耗速度的影响进行了数值分析。0.9、0.7和0.5的当量比,燃料混合物成分从纯甲烷到纯氢气,被认为涵盖了贫区的广泛条件。产品侧有热损失的一维不对称逆流预混层流火焰(aCFPF)被视为代表湍流火焰基本单元的小火焰配置,消耗速度用于表征应变和热损失的影响。由于多组分混合物消耗速度的定义不明确,因此对两种定义进行了比较。第一个定义基于燃料种类的消耗率的加权组合,第二个定义基于全局热释放率。与基于燃料消耗的定义相比,基于热释放的消耗速度的定义导致一些甲烷-氢气-空气混合物的拉伸火焰速度的值更低,甚至对应变率的响应相反。应变速率导致贫甲烷-氢气混合物的火焰速度增加,达到最大值,之后火焰速度随着应变速率而降低。热损失降低了拉伸火焰的速度,并由于应变和热损失的结合而导致小火焰更快地熄灭。氢气添加量和当量比显著影响最大消耗速度和火焰对组合应变速率和热损失的响应。还分析了氢气对混合物热扩散性能的影响,其特征为Zeldovich数和有效Lewis数,并与对消耗速度的影响有关。根据aCFPF的结果,对多组分燃料混合物的路易斯数的两个定义进行了评估。
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引用次数: 1
Flame speed in diffusion dominated premixed flames 扩散过程中火焰速度主导预混火焰
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-11-12 DOI: 10.1080/13647830.2022.2143428
F. Vance, J. van Oijen, L. D. de Goey
Development of a premixed flame theory that includes the effects of flame stretch and curvature has been at the forefront of combustion research. Diffusion dominated flames such as highly curved flame balls present a challenging flame structure that has not been included in current flame stretch theory so far. In such flames, the relationship between consumption speed and negative displacement speed usually marks the boundary of what flame stretch theory can predict. In this work, our objective is to derive a general formulation which naturally includes this relationship. We use flamelet equations derived using a mass based stretch rate and show that if the diffusion flux at the unburnt side is not ignored, as is normally done in flame stretch theory, a formulation that can describe the propagation of different types of premixed flames can be derived. Based on the thin reaction zone assumption, solutions from theory are verified against numerical results for 1D ideal flame balls. Further verification is done for multi-dimensional ball-like flames, where both convection and diffusion dominated regions are present for highly curved flames. It is shown that the extended theory is able to predict the flame kinematics in a better way by describing the diffusion dominated flame propagation as well.
考虑火焰拉伸和曲率影响的预混燃烧理论的发展一直是燃烧研究的前沿。以扩散为主导的火焰,如高弯曲的火焰球,是一种具有挑战性的火焰结构,目前还没有包括在火焰拉伸理论中。在这种火焰中,消耗速度与负位移速度之间的关系通常标志着火焰拉伸理论可以预测的边界。在这项工作中,我们的目标是推导一个自然包含这种关系的一般公式。我们使用基于质量拉伸率的小火焰方程,并表明如果不忽略未燃烧侧的扩散通量,就像火焰拉伸理论中通常做的那样,可以推导出一个可以描述不同类型预混火焰传播的公式。在薄反应区假设的基础上,对一维理想火焰球的理论解与数值结果进行了验证。进一步验证了多维球状火焰,其中对流和扩散主导区域存在于高度弯曲的火焰中。结果表明,该推广理论能够较好地描述以扩散为主的火焰传播过程,从而预测火焰的运动特性。
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引用次数: 0
A simplified two-mixture-fraction-based flamelet modelling and its validation on a non-premixed staged combustion system 基于两种混合物分数的简化小火焰模型及其在非预混分级燃烧系统中的验证
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-11-11 DOI: 10.1080/13647830.2022.2144460
Panlong Yu, H. Watanabe
A simplified two-mixture-fraction-based flamelet model is proposed in this work for a non-premixed staged combustion mode in which three feeds are introduced into the flow field. As the third stream is injected downstream of the main port, the system can be considered a special case of the two-mixture-fraction-based systems. It is considered that if a well-mixing is achieved in the upper stream prior to the third-stream injection, the simplification of the two-mixture-fraction-based flamelet model is feasible. In this work, a simplified model is proposed which can greatly reduce the library size compared to the complete two-mixture-fraction-based flamelet library providing identical resolutions for the fuel stream mixture fraction and the progress variable, respectively. Analysis associated with the interpolation strategy has been implemented. Extension of the current model for the cases in which the well-mixing state is not attained is also analysed, as well as the consideration of heat loss. To validate the model, two adiabatic cases of two-dimensional (2D) direct numerical simulations (DNS) have been performed in this work. To describe the chemical events, one is using finite-rate chemistry (FRC), while the other one is realised by means of the current flamelet model (FLM). An a priori test case that directly looks up the libraries by using the tracking parameters obtained from the FRC case is also considered. It is observed that the interpolation along the primary oxidiser mixture fraction direction outperforms that along directions for both fuel and primary oxidiser mixture fractions. It is also found that three one-mixture-fraction-based flamelet libraries which form the current model are sufficient for simulation of the non-premixed staged combustion, while the extended one which composes five libraries is expected to gain higher accurateness. In the FLM case, although the distributions of tracking parameters deviate from the FRC case slightly, good agreements can be obtained in terms of temperature and species mass fractions. The a priori test shows that the current model can reproduce the reacting flow accurately when the tracking parameters are identical to the FRC case. It is confirmed that the current model can be used to predict the characteristics of the reacting flow in the non-premixed staged combustion.
针对流场中引入三种进料的非预混分级燃烧模式,提出了一种简化的基于两种混合物分数的小火焰模型。由于第三股流被注入主端口的下游,该系统可以被视为两种基于混合物馏分的系统的特殊情况。认为如果在第三次流注入之前在上游实现良好混合,则简化基于两种混合物分数的小火焰模型是可行的。在这项工作中,提出了一个简化模型,与完全的基于两种混合物分数的小火焰库相比,该模型可以大大减小库的大小,分别为燃料流混合物分数和进度变量提供相同的分辨率。已经实施了与插值策略相关的分析。还分析了当前模型在未达到充分混合状态的情况下的扩展,以及热损失的考虑。为了验证该模型,本工作中进行了二维(2D)直接数值模拟(DNS)的两种绝热情况。为了描述化学事件,一种是使用有限速率化学(FRC),而另一种是通过当前的小火焰模型(FLM)实现的。还考虑了通过使用从FRC案例中获得的跟踪参数来直接查找库的先验测试案例。观察到,对于燃料和一次氧化剂混合物馏分,沿着一次氧化器混合物馏分方向的插值优于沿着方向的插值。研究还发现,构成当前模型的三个基于一混合物分数的小火焰库足以模拟非预混阶段燃烧,而由五个库组成的扩展小火焰库有望获得更高的精度。在FLM情况下,尽管跟踪参数的分布与FRC情况略有偏差,但在温度和物种质量分数方面可以获得良好的一致性。先验检验表明,当跟踪参数与FRC情况相同时,当前模型可以准确地再现反应流。结果表明,该模型可用于预测非预混分级燃烧中反应流的特性。
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引用次数: 2
A modified thickened flame model for simulating extinction 模拟熄灭的改进加厚火焰模型
IF 1.3 4区 工程技术 Q4 ENERGY & FUELS Pub Date : 2022-11-10 DOI: 10.1080/13647830.2022.2141138
Adam L. Comer, T. Gallagher, K. Duraisamy, B. Rankin
For large-eddy simulation of turbulent premixed reacting flows, major challenges stem from the inability to resolve the flame in a computationally affordable manner. These challenges are most evident in combustors characterized by large domains and thin flames. In these applications, the thickened flame model may be used to extend the flame artificially to a numerically resolvable size through a thickening factor. Thicker flames exhibit suppressed wrinkling in the presence of turbulence, so an efficiency factor increases the flame speed without influencing flame thickness. In contrast to the detailed considerations of unresolved turbulent flame wrinkling, recent work shows that thickened flames do not respond correctly to resolved-scale stretch. In this work, errors in stretch-induced extinction are considered. The already established effect of thickening on extinction is illustrated, and the effect of efficiency factor is characterized in detail. Significant errors in extinction stretch rate are observed analytically and numerically in twin premixed counterflow flame simulations. In general, the original thickened flame formulation does not permit control over extinction, in contrast to its control over freely-propagating-flame thickness and speed. For reactant mixtures with a Lewis number greater than 1, a novel modification of the thickened flame formulation is presented, and through Lewis number adjustments, extinction errors are significantly reduced, while key flame thickening and speed properties of the original formulation are preserved. A test case featuring a turbulent premixed bluff-body-stabilized flame demonstrates that the extinction errors of the original formulation can lead to premature blowoff dynamics and significant statistical errors, if the grid is too coarse. The modified thickened flame model applied to the same grids addresses this issue and provides reasonable flame predictions on all grids, indicating the potential for extending this combustion model to resolutions of greater engineering relevance.
对于湍流预混合反应流的大涡模拟,主要挑战源于无法以计算上可负担的方式解析火焰。这些挑战在以大面积和细火焰为特征的燃烧器中最为明显。在这些应用中,增稠火焰模型可以用于通过增稠因子将火焰人为地扩展到数值上可分辨的尺寸。较厚的火焰在存在湍流的情况下表现出抑制的褶皱,因此效率因子在不影响火焰厚度的情况下增加了火焰速度。与未解决的湍流火焰褶皱的详细考虑相反,最近的工作表明,增厚的火焰对已解决的尺度拉伸没有正确响应。在这项工作中,考虑了拉伸引起的消光的误差。说明了增稠对消光的影响,并详细描述了效率因子的影响。在双预混逆流火焰模拟中,从分析和数值上观察到消光拉伸率的显著误差。通常,与控制自由传播的火焰厚度和速度相比,原始增稠火焰配方不允许控制熄灭。对于路易斯数大于1的反应混合物,提出了对增稠火焰配方的新改性,通过路易斯数的调整,消光误差显著降低,同时保留了原始配方的关键火焰增稠和速度特性。一个以湍流预混钝体稳定火焰为特征的测试案例表明,如果网格过于粗糙,原始配方的消光误差可能导致过早的井喷动力学和显著的统计误差。应用于相同网格的改进的增稠火焰模型解决了这一问题,并在所有网格上提供了合理的火焰预测,这表明有可能将该燃烧模型扩展到具有更大工程相关性的分辨率。
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Combustion Theory and Modelling
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