Effects of compositional fluctuations on premixed flames
Effects of compositional fluctuations on premixed flames
复制标题
成分波动对预混火焰的影响
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
R. Cant
中科院分区：
文献类型：
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作者：
R. Grout;N. Swaminathan;R. Cant
采用完全可压缩直接数值模拟（DNS）方法研究了具有简化多步化学反应的褶皱小火焰区（ReΛ = 38，u′/SL = 0.7，Da = 2.3）的分层湍流预混火焰的行为。层流预混火焰在初始静止域传播到湍流，使标量场和速度场正确耦合。分层情况（0.4 < φ < 1.2）与均匀情况的比较表明，在这种情况下，由于传播速度不同，火焰前缘的湍流增强，从而使湍流火焰速度增加。优先传播到更易燃的混合物中导致混合物分数和进展变量之间的相关性，特别是在火焰刷的前缘处。在火焰前面，成分梯度优先与最大的压缩应变对齐。在火焰前锋，进步可变梯度优先对齐最广泛的湍流应变，并在火焰的后一部分的混合物分数梯度和最压缩的主应变之间的对齐恶化。尽管如此，通过假设混合物分数和进度变量的统计独立性来方便地近似联合pdf，不会在反应速率的近似中引入显著的误差。
Fully compressible direct numerical simulation (DNS) is used to study the behaviour of a stratified turbulent premixed flame in the wrinkled flamelet regime (ReΛ = 38, u′/S L = 0.7, Da = 2.3) with reduced multi-step chemistry. A laminar premixed flame in an initially quiescent domain propagates into a turbulent flow so that the scalar and velocity fields are correctly coupled. Comparison of a stratified scenario (0.4 < φ < 1.2) with an otherwise identical homogeneous case indicates that in this regime the turbulent flame speed is increased by enhanced flame front wrinkling as a result of differential propagation speeds. The preferential propagation into more combustible mixture results in a correlation between the mixture fraction and progress variable, particularly at the leading edge of the flame brush. In front of the flame, the composition gradient preferentially aligns with the most compressive strain. Within the flame front, the progress variable gradient preferentially aligns with the most extensive turbulent strain, and in the latter portion of the flame the alignment between the mixture fraction gradient and the most compressive principal strain deteriorates. Despite this, the convenient approximation of the joint pdf by assuming statistical independence of the mixture fraction and progress variable does not introduce a significant error in the approximation of the reaction rates.