Effect of heat release on turbulence and scalar-turbulence interaction in premixed combustion
Effect of heat release on turbulence and scalar-turbulence interaction in premixed combustion
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DOI：
10.1063/1.2896285
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发表时间：
2008-03-01
影响因子：
4.6
通讯作者：
Swaminathan, N.
中科院分区：
文献类型：
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作者：
Hartung, G.;Hult, J.;Swaminathan, N.
采用立体粒子图像测速技术和平面激光诱导荧光技术同时测量了稳定在海崖体上的乙烯-空气预混火焰的局部湍流强度和火焰前沿位置。三种不同的当量比，0.55，0.63和0.7，和三个不同的雷诺数，14 000，17 000和21 000，被认为是。在上述范围内和相应的冷流中，对五种不同的火焰结构进行了激光测量。通过对比冷、热流的测量结果，研究了放热对湍流及其与火焰前缘相互作用的影响。所有的火焰都在薄反应区区域。在冷流中观察到在海崖体后面形成的典型流动特征，而在反应流中，海崖体后面的再循环涡流的平均速度以及因此的形状、尺寸和特性受到热释放的强烈影响。穿过平均火焰的强加速度和再循环涡流的停滞平面的径向向外移动产生负的径向速度，这在相应的冷流情况下是不存在的。火焰前缘的空间不规则性导致湍流动能的增加。虽然应变率张量e（ij）组件的平均值和均方根值的减少被观察到的反应的情况下，正如人们所期望的那样，在火焰前端的局部流动加速导致的偏度和峰度的概率密度函数（PDF）的e（ij）组件的大幅增加。通过分析火焰前缘法线与e（ij）的特征向量的取向，研究了湍流与标量的相互作用。这个方向的PDF清楚地表明，法线具有与广泛应变率对齐的增加的趋势，这意味着标量梯度被湍流破坏，因为标量等值面被拉开。这一结果质疑了常用于预混火焰建模的被动标量湍流物理学的有效性。然而，刘易斯数对这种排列行为的影响目前尚不清楚。(c)2008年美国物理研究所。
Stereoscopic particle image velocimetry and planar laser induced fluorescence measurements of hydroxyl radical are simultaneously applied to measure, respectively, local turbulence intensities and flame front position in premixed ethylene-air flames stabilized on a bluff body. Three different equivalence ratios, 0.55, 0.63, and 0.7, and three different Reynolds numbers, 14 000, 17 000, and 21 000, are considered. Laser measurements were made for five different flame configurations within the ranges above and in the corresponding cold flows. By comparing the measurements of the cold and the corresponding hot flows, the effect of heat release on the turbulence and its interaction with the flame front is studied. All the flames are in the thin reaction zone regime. Typical flow features forming behind the bluff body are observed in the cold flows, whereas in the reacting flows the mean velocities and thus the shape, size, and characteristics of the recirculating eddy behind the bluff body are strongly influenced by the heat release. The strong acceleration across the mean flame and the radial outward shift of the stagnation plane of the recirculating eddy yield negative radial velocities which are absent in the corresponding cold flow cases. The spatial intermittency of the flame front leads to an increase in the turbulent kinetic energy. Although a decrease in the mean and rms values of the strain rate tensor e(ij) components is observed for the reacting case as one would expect, the local flow acceleration across the flame front leads to a substantial increase in the skewness and the kurtosis of the probability density functions (PDFs) of e(ij) components. The turbulence-scalar interaction is studied by analyzing the orientation of the flame front normal with the eigenvectors of e(ij). The PDFs of this orientation clearly show that the normals have an increased tendency to align with the extensive strain rate, which implies that the scalar gradients are destroyed by the turbulence as the scalar isosurfaces are pulled apart. This result questions the validity of passive scalar turbulence physics commonly used for premixed flame modeling. However, the influence of Lewis number on this alignment behavior is not clear at this time. (c) 2008 American Institute of Physics.