Small Scale Features of Velocity and Scalar Fields in Turbulent Premixed Flames
Small Scale Features of Velocity and Scalar Fields in Turbulent Premixed Flames
复制标题
湍流预混火焰中速度场和标量场的小尺度特征
DOI：
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
T. Hasegawa
中科院分区：
文献类型：
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作者：
A. Mura;V. Robin;M. Champion;T. Hasegawa
由于湍流混合的最终阶段发生在雷诺平均Navier Stokes（RANS）或湍流反应流的大涡模拟（LES）方法中未解决的尺度上，因此分子耗散率的封闭仍然是湍流燃烧领域的一个重要问题。在本研究中，湍流火焰与预混反应物被认为是在湍流预混燃烧的小火焰区：Damköhler和Karlovitz数的值是这样的Da > 1和Ka < 1。在这种情况下，混合速率显然取决于湍流特性，但也强烈地受到层流小火焰结构的影响，该结构驱动反应性物质的瞬时梯度。在目前的工作中，分析集中在一些不同的未封闭的条款中出现的平均反应标量耗散率的输运方程。新的封闭依赖于快速化学假设，提出了这些生产条款和现有模型的异同进行了讨论。以前的工作致力于标量耗散率的建模最近表明，反应功能和膨胀现象强烈影响的行为，一些条款相对于被动标量情况的参考，本研究证实了这些发现的相关性。最后，考虑直接数值模拟（DNS）数据库来评估所提出模型的有效性。这些DNS对应于对于气体膨胀因子τ=（Tb-Tu）/Tu的三个不同值（即1.5、4和6.5）获得的三维统计稳定的平面湍流预混火焰的计算，其中下标u和B分别指未燃烧的反应物和燃烧产物。相对于以前的研究，这些数据允许详细检查不同的建模建议的有效性时，气体膨胀系数是不同的。
Because the ultimate stages of turbulent mixing take place at the unresolved scales in either Reynolds Average Navier Stokes (RANS) or Large Eddy Simulation (LES) approaches of turbulent reactive flows, the closure of molecular dissipation rates still remains an essential problem in the field of turbulent combustion. In the present study, turbulent flames with premixed reactants are considered in the flamelet regime of turbulent premixed combustion: Damköhler and Karlovitz number’s values are such that Da > 1 and Ka < 1. In this situation, the mixing rate clearly depends upon the turbulence characteristics but is also strongly influenced by the laminar flamelet structures that drive the instantaneous gradients of the reactive species. In the present work, the analysis is focused on some among the different unclosed terms that arise in the transport equation of the mean reactive scalar dissipation rate. New closures relying on the fast chemistry assumptions are proposed for these production terms and similarities and differences with existing models are discussed. Previous works devoted to the modeling of the scalar dissipation rate have recently shown that both reactive features and expansion phenomena strongly influence the behavior of some terms with respect to the passive scalar situation of reference, and the present study confirms the relevance of these findings. Finally, Direct Numerical Simulation (DNS) databases are considered to assess the validity of the proposed models. These DNS correspond to the calculations of three-dimensional statistically steady planar turbulent premixed flames obtained for three distinct values of the gas expansion factor τ=(Tb − Tu)/Tu namely 1.5, 4 and 6.5, where subscripts u and b refer to unburned reactants and burned products respectively. With respect to previous studies, these data allow a detailed check of the validity of the different modeling proposals when the gas expansion factor is varied.
影响因子：
4.6
作者：
N. Chakraborty;N. Swaminathan
通讯作者：
N. Chakraborty;N. Swaminathan