Influence of the Damkohler number on turbulence-scalar interaction in premixed flames. I. Physical insight
Influence of the Damkohler number on turbulence-scalar interaction in premixed flames. I. Physical insight
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DOI：
10.1063/1.2714070
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发表时间：
2007-04-01
影响因子：
4.6
通讯作者：
Swaminathan, N.
中科院分区：
文献类型：
--
作者：
Chakraborty, N.;Swaminathan, N.
标量耗散率与反应速率密切相关，是湍流火焰模拟中的一个核心量。众所周知，湍流-标量相互作用在标量混合的湍流中起着至关重要的作用，从而对标量耗散率起着至关重要的作用。这个相互作用过程的特点是由标量梯度矢量和湍流应变率张量之间的张量内积，它被发现强烈依赖于达姆科勒数，Da。两个直接的数值模拟数据集进行了详细分析，以了解Da依赖的物理。在低Damkohler数（Da < 1）的火焰中，标量梯度与最大压缩主应变率的一致性导致湍流产生标量梯度，而在高Da火焰中，湍流耗散了标量梯度。这种耗散的标量梯度在高Da火焰是因为其优先与最广泛的主应变速率对齐。即使对于Da < 1的火焰，在强烈的热释放的区域中，标量梯度具有与最广泛的应变速率对齐的趋势。这种明显的变化是由于化学应变率之间的强烈竞争，由于膨胀从火焰前锋和局部流体动力学应变率。对齐特性影响火焰法向和切向应变率统计。当Da > 1时，火焰法向应变速率在整个火焰刷中为正，而当Da < 1时，火焰法向应变速率主要为负。尽管存在这种差异，平均切向应变率仍然是正的，从而产生火焰表面积生产。然而，生产结果通过不同的物理机制。这些差异的湍流预混火焰的建模可能产生的影响进行了识别和解释。(c)2007年美国物理学会
Scalar dissipation rate is a central quantity in turbulent flame modeling as it is closely related to the reaction rate. It is well known that turbulence-scalar interaction plays a vital role in turbulent flows with scalar mixing and thus on the scalar dissipation rate. This interaction process is characterized by the tensor inner product between the scalar gradient vector and the turbulence strain rate tensor and it is found to depend strongly on the Damkohler number, Da. Two direct numerical simulation data sets are analyzed in detail in order to understand the physics of Da dependence. The well known alignment of scalar gradient with the most compressive principal strain rate resulting in production of the scalar gradient by turbulence is observed for low (Da < 1) Damkohler number flame, whereas the turbulence dissipates the scalar gradient in high Da flame. This dissipation of the scalar gradient in the high Da flame is because of its preferential alignment with the most extensive principal strain rate. Even for Da < 1 flame, in the regions of intense heat release the scalar gradient has a tendency to align with the most extensive strain rate. This distinct change is because of strong competition between chemical strain rate, due to dilatation from the flame front and the local fluid dynamic strain rate. The alignment characteristics affect flame normal and tangential strain rate statistics. The flame normal strain rate is found to be positive throughout the flame brush when Da > 1, whereas it is predominantly negative when Da < 1. Despite this difference the mean tangential strain rate remains positive yielding flame surface area production. However, the production results via different physical mechanisms. Possible implications of these differences on the modeling of turbulent premixed flames are identified and explained.(c) 2007 American Inst of Phys.