Investigation of the influence of combustion-induced thermal expansion on two-point turbulence statistics using conditioned structure functions
Investigation of the influence of combustion-induced thermal expansion on two-point turbulence statistics using conditioned structure functions
复制标题
使用条件结构函数研究燃烧引起的热膨胀对两点湍流统计的影响
DOI：
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发表时间：
2019
影响因子：
3.7
通讯作者：
T. Hasegawa
中科院分区：
文献类型：
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作者：
V. Sabelnikov;A. Lipatnikov;S. Nishiki;T. Hasegawa
速度场的二阶结构函数（SF）表征两点的速度差，广泛应用于无反应湍流的研究。在本文中，该方法得到扩展，以研究燃烧引起的热膨胀对预混火焰刷内湍流的影响。为此，本文介绍了在两个不同点（反应物-反应物、反应物-产物、产物-产物等）条件下混合状态的各种组合的SF，并在附录中推导了相关的精确传输方程。随后，为了证明新开发的方法促进对湍流反应流的理解的能力，从三维（3-D）直接数值模拟数据中提取条件SF，这些数据是从两个统计一维平面、完全发展、弱湍流、预混合、单步化学火焰获得的，其特征是密度比显着不同（7.53和2.50），而所有其他条件大致相等。获得的结果表明，调节后的 SF 与标准平均 SF 显着不同，并且传达了有关燃烧引起的热膨胀对湍流影响的各种局部现象的大量重要信息。特别是，条件SF不仅（i）表明了论文中讨论的许多已知的局部现象，而且（ii）揭示了一种不太被认识的现象，例如燃烧引起的热膨胀对恒定密度未燃烧反应物中湍流的重大影响，甚至（iii）使我们能够检测到一种新现象，例如小火焰内出现的强烈的局部速度扰动（剪切层）。此外，以热释放区为条件的SF表明燃烧引起的热膨胀对小火焰内小规模两点速度差的演变具有高度各向异性影响，对于局部速度矢量的不同分量，影响是相反的（增加或减少）。
The second-order structure functions (SFs) of the velocity field, which characterize the velocity difference at two points, are widely used in research into non-reacting turbulent flows. In the present paper, the approach is extended in order to study the influence of combustion-induced thermal expansion on turbulent flow within a premixed flame brush. For this purpose, SFs conditioned to various combinations of mixture states at two different points (reactant–reactant, reactant–product, product–product, etc.) are introduced in the paper and a relevant exact transport equation is derived in the appendix. Subsequently, in order to demonstrate the capabilities of the newly developed approach for advancing the understanding of turbulent reacting flows, the conditioned SFs are extracted from three-dimensional (3-D) direct numerical simulation data obtained from two statistically 1-D planar, fully developed, weakly turbulent, premixed, single-step-chemistry flames characterized by significantly different (7.53 and 2.50) density ratios, with all other things being approximately equal. Obtained results show that the conditioned SFs differ significantly from standard mean SFs and convey a large amount of important information on various local phenomena that stem from the influence of combustion-induced thermal expansion on turbulent flow. In particular, the conditioned SFs not only (i) indicate a number of already known local phenomena discussed in the paper, but also (ii) reveal a less recognized phenomenon such as substantial influence of combustion-induced thermal expansion on turbulence in constant-density unburned reactants and even (iii) allow us to detect a new phenomenon such as the appearance of strong local velocity perturbations (shear layers) within flamelets. Moreover, SFs conditioned to heat-release zones indicate a highly anisotropic influence of combustion-induced thermal expansion on the evolution of small-scale two-point velocity differences within flamelets, with the effects being opposite (an increase or a decrease) for different components of the local velocity vector.