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首页> 外文期刊>International journal of numerical methods for heat & fluid flow >Unsteady RANS and scale adaptive simulations of a turbulent spray flame in a swirled-stabilized gas turbine model combustor using tabulated chemistry
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Unsteady RANS and scale adaptive simulations of a turbulent spray flame in a swirled-stabilized gas turbine model combustor using tabulated chemistry

机译：基于列表化学的涡旋稳定燃气轮机模型燃烧室湍流喷雾火焰的非定常RANS和尺度自适应模拟

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Purpose - The purpose of this paper is to numerically investigate the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor using the commercial computational fluid dynamic (CFD) software ANSYS FLUENT. The first scope of the study aims to explicitly compare the predictive capabilities of two turbulence models namely Unsteady Reynolds Averaged Navier-Stokes and Scale Adaptive Simulation for a reasonable trade-off between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium(NEQ) effects caused by turbulent strain such as flame stretching. Design/methodology/approach - Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases, respectively. The computing method includes a two-way coupling in which phase properties and spray source terms are interchanging between the two phases within each coupling time step. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane + toluene) are used as jet-A1 surrogates. The combustion model is based on the mean mixture fraction and its variance, and a presumed-probability density function is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the equilibrium (EQ) assumption and thereafter, detailed NEQ calculations through the steady flamelets concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1,045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0 using a sensitivity based method, Alternate Species Elimination. Findings - Numerical results of the gas velocity, the gas temperature and the species molar fractions are compared with their experimental counterparts obtained from a steady state flame available in the literature. It is observed that, SAS coupled to the tabulated flamelet-based chemistry, predicts reasonably the main flame trends, while URANS even provided with the same combustion model and computing resources, leads to a poor prediction of the global flame trends, emphasizing the asset of a proper resolution when simulating spray flames. Research limitations/implications - The steady flamelet model even coupled with a robust turbulence model does not reproduce accurately the trend of species with slow oxidation kinetics such as CO and H2, because of the restrictiveness of the solutions space of flamelet equations and the assumption of unity Lewis for all species. Practical implications - This work is adding a contribution for spray flame modeling and can be seen as an extension to the significant efforts for the modeling of gaseous flames using robust turbulence models coupled with the tabulated flamelet-based chemistry approach to considerably reduce computing cost. The exclusive use of a commercial CFD code widely used in the industry allows a direct application of this simulation approach to industrial configurations while keeping computing cost reasonable. Originality/value - This study is useful to engineers interested in designing combustors of gas turbines and others combustion systems fed with liquid fuels.
机译：目的-本文的目的是使用商用计算流体力学（CFD）软件ANSYS FLUENT对比例缩放的旋流稳定型燃气轮机燃烧器的三维（3D）反应湍流两相流场进行数值研究。本研究的第一个范围旨在明确比较两种湍流模型（非稳态雷诺平均Navier-Stokes和尺度自适应仿真）的预测能力，以便在应用于模拟旋流稳定的喷雾时在结果精度和总体计算成本之间进行合理的权衡燃烧。研究的第二个范围是使用真实的化学模型将化学反应耦合到湍流，并且还模拟由湍流应变（例如火焰拉伸）引起的局部化学非平衡（NEQ）效应。设计/方法/方法-标准欧拉公式和拉格朗日公式分别用于描述气相和液相。该计算方法包括双向耦合，其中在每个耦合时间步长内，相特性和喷雾源项在两个相之间互换。所使用的燃料是液体射流A1，它以多分散喷雾的形式喷射，并且使用无限电导率模型计算液滴的蒸发速率。单组分（正癸烷）和二组分燃料（正癸烷+甲苯）用作喷气A1替代物。燃烧模型基于平均混合物分数及其方差，并且使用假定的概率密度函数对湍流-化学相互作用进行建模。通过首先使用平衡（EQ）假设，然后使用稳定小火焰概念进行详细的NEQ计算，来确定化学表格所需的瞬时热化学状态。这些替代物的燃烧化学反应是通过减少的化学动力学机理（CKM）来表示的，其中包括139种反应中的1,045个反应，该反应来自详细的jet-A1替代模型JetSurf 2.0，使用基于灵敏度的方法，替代物种消除。发现-将气体速度，气体温度和物质摩尔分数的数值结果与从稳态火焰中获得的文献中的实验结果进行比较。可以看出，SAS与基于表格的基于火焰的化学反应相结合，可以合理地预测主要火焰趋势，而URANS甚至提供相同的燃烧模型和计算资源，也会导致对整体火焰趋势的预测不佳，从而强调了模拟喷雾火焰时的适当分辨率。研究局限/意义-稳定的小火焰模型，甚至与鲁棒的湍流模型相结合，也无法准确再现具有慢氧化动力学的物种（如CO和H2）的趋势，因为小火焰方程的解空间有限且假设为单位刘易斯所有物种。实际意义-这项工作为喷雾火焰建模做出了贡献，可以看作是对使用健壮湍流模型以及基于表格的基于小火焰的化学方法显着降低计算成本的气态火焰建模所做的巨大努力的扩展。在行业中广泛使用的商业CFD代码的排他性使用可以将该模拟方法直接应用于工业配置，同时保持合理的计算成本。原创性/价值-这项研究对有兴趣设计燃气轮机燃烧器和其他以液体燃料为燃料的燃烧系统的工程师有用。

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