A DNS study of extreme and leading points in lean hydrogen-air turbulent flames-part II: Local velocity field and flame topology
A DNS study of extreme and leading points in lean hydrogen-air turbulent flames-part II: Local velocity field and flame topology
复制标题
稀氢空气湍流火焰极值点和主导点的 DNS 研究-第二部分：局部速度场和火焰拓扑
DOI：
10.1016/j.combustflame.2021.111712
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发表时间：
2022
影响因子：
4.4
通讯作者：
Lipatnikov Andrei N.
中科院分区：
文献类型：
--
作者：
Lee HsuChew;Dai Peng;Wan Minping;Lipatnikov Andrei N.
最近的直接数值模拟（Lee et al.）获得的数据在统计上是一维的，为了探索(i)以峰值（在计算域上）燃料消耗率（FCR）或热释放率（HRR）为特征的极值点和（ii）以高FCR或HRR为特征的领先点的局部特征和结构，进一步分析了三个不同Karlovitz数K（3到33）为特征的复杂化学氢-空气火焰，这些点也以高FCR或HRR为特征，但最远进入未燃烧的反应物。结果表明：一方面，火焰扰动的共同特征（曲率、应变和拉伸率、位移速度）在极端点或超前点、FCR点或HRR点上波动显著，且在不同火焰中有所不同；此外，其他两点局部量，如燃烧过程变量的局部梯度或物质（如自由基H）质量分数在不同的火焰中是不同的。因此，一个普通的扰动层流火焰的简单配置不能作为在不同K a处所讨论的点周围区域的整个局部结构的通用模型。另一方面，在所有三种湍流火焰和临界应变平面层流火焰中，FCR极端点的单点局部特征（温度、物质质量分数、它们的产生速率）是可比较的。特别是，极端点的FCR波动微弱，彼此近似相等，并与临界应变层流火焰的峰值FCR相等。后一项发现意味着：(i)在临界应变层流火焰中评估的最大FCR可以用于表征湍流火焰中极端点或先导点的局部FCR，从而支持先导点概念；（ii）几乎相同的极端FCR可以在本质上不同的局部燃烧结构中达到。
Data obtained in recent direct numerical simulations (Lee et al.) of statistically one-dimensional and planar, lean complex-chemistry hydrogen-air flames characterized by three different Karlovitz numbers K a ranging from 3 to 33 are further analyzed in order to explore local characteristics and structure of (i) extreme points characterized by the peak (over the computational domain) Fuel Consumption Rate (FCR) or Heat Release Rate (HRR) and (ii) leading points that are also characterized by a high FCR or HRR, but advance furthest into unburned reactants. Results show that, on the one hand, common characteristics of flame perturbations (curvature, strain and stretch rates, displacement speed) fluctuate significantly in the extreme or leading, FCR or HRR points and are different in different flames. Moreover, other two-point local quantities such as the local gradients of combustion progress variables or species (eg, the radical H) mass fractions are different in different flames. Therefore, a common simple configuration of a perturbed laminar flame cannot be used as a catchall model of the entire local structure of zones surrounding the discussed points at various K a. On the other hand, single-point local characteristics (temperature, species mass fractions, rates of their production) of the FCR extreme points are comparable in all three turbulent flames and in the critically strained planar laminar flame. In particular, the FCRs in the extreme points fluctuate weakly and are approximately equal to each other and to the peak FCR in the critically strained laminar flame. The latter finding implies that (i) the maximum FCR evaluated in the critically strained laminar flame could be used to characterize, in a first approximation, the local FCR in the extreme or leading points in turbulent flames, thus, supporting the leading point concept, and (ii) almost the same extreme FCR can be reached in substantially different local burning structures.