Framework for simulating stationary spherical flames
Framework for simulating stationary spherical flames
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DOI：
10.1016/j.proci.2020.06.013
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
F. Ruiz;Guillaume Beardsell;G. Blanquart
中科院分区：
文献类型：
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作者：
F. Ruiz;Guillaume Beardsell;G. Blanquart
理解和量化火焰拉伸率对层流火焰速度和火焰结构的影响，从解释实验测量的层流燃烧速度到表征湍流对预混火焰的影响起着重要作用。不幸的是，考虑这些影响往往需要一个非定常反应流求解器，可能是计算昂贵的。在这项工作中，我们提出了一个数学框架来进行模拟的固定球形火焰。目标是通过执行坐标变化来保持火焰在恒定的半径（并且因此保持恒定的拉伸速率）。在新的火焰附着的参考框架中的控制方程类似于自由传播的球形火焰的原始方程。唯一的区别是存在额外的源项，其目的是驱动数值解的稳定状态。这些源项涉及一个自由参数：火焰拉伸速率，其可以在真实的时间中计算或由用户施加。该参数最终控制稳态火焰半径和稳态火焰速度。这就是为什么在给定的拉伸率下，静止球形火焰模拟的结果与自由膨胀球形火焰的结果相匹配。作为一个例子，层流火焰速度对拉伸速率的依赖性是杠杆提取Markstein长度为氢/空气混合物在不同的当量比，以及烃/空气混合物（CH 4和C7 H16）。数值预测与实验测量结果吻合良好（实验不确定性范围内）。最后，所提出的方法在化学动力学软件FlameMaster中实现。使用一个专用的稳态求解器与非均匀优化网格导致显着降低计算成本，突出表明，所提出的方法是非常适合其他化学动力学软件，如Chemkin/预混料和Cantera。
Understanding and quantifying the effects of flame stretch rate on the laminar flame speed and flame structure plays an important role from interpreting experimentally-measured laminar burning velocities to characterizing the impact of turbulence on premixed flames. Unfortunately, accounting for these effects often requires an unsteady reacting flow solver and may be computationally expensive. In this work, we propose a mathematical framework to perform simulations of stationary spherical flames. The objective is to maintain the flame at a constant radius (and hence a constant stretch rate) by performing a coordinate change. The governing equations in the new flame-attached frame of reference resemble the original equations for freely-propagating spherical flames. The only difference is the presence of additional source terms whose purpose is to drive the numerical solution to a steady state. These source terms involve one free parameter: the flame stretch rate, which may either be computed in real time or imposed by the user. This parameter controls ultimately the steady state flame radius and the steady state flame speed. That is why, at a given stretch rate, the results of the stationary spherical flame simulations match those of a freely-expanding spherical flame. As an illustration, the dependence of the laminar flame speed on the stretch rate is leveraged to extract Markstein lengths for hydrogen/air mixtures at different equivalence ratios, as well as for hydrocarbon/air mixtures (CH4and C7H16). Numerical predictions are in good agreement with experimental measurements (within experimental uncertainties). Finally, the proposed methodology is implemented in the chemical kinetic software FlameMaster. The use of a dedicated steady-state solver with a non-uniform optimized mesh leads to significant reductions in the computational cost, highlighting that the proposed methodology is ideally suited for other chemical kinetic software such as Chemkin/Premix and Cantera.