Heat release effects on the Reynolds stress budgets in turbulent premixed jet flames at low and high Karlovitz numbers
Heat release effects on the Reynolds stress budgets in turbulent premixed jet flames at low and high Karlovitz numbers
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DOI：
10.1016/j.combustflame.2020.02.014
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发表时间：
2020-06-01
影响因子：
4.4
通讯作者：
Mueller, Michael E.
中科院分区：
文献类型：
--
作者：
Lee, Jinyoung;MacArt, Jonathan F.;Mueller, Michael E.
在低卡洛维茨数的湍流预混火焰中，燃烧放热对湍流有重要影响。火焰中的热膨胀引起膨胀，相应的压力-膨胀关系是湍流动能的主要来源。因此，法向雷诺应力的火焰法向分量显著增加。此外，对于剪切火焰，典型的喷流火焰，雷诺应力的剪切分量表现出反Boussinesq行为。对于低卡洛维茨数的火焰，这些影响占主导地位，没有一个模型能够成功地预测所有雷诺应力分量。为了建立更完整的湍流模型，需要分析热释放对所有雷诺应力分量演化的影响。在这项工作中，雷诺应力预算是从空间演化的低卡洛维茨数和高卡洛维茨数的湍流预混平面射流火焰的直接数值模拟(DNS)数据库中获得的。在雷诺应力预算中，速度-压力梯度关联项在两个卡洛维茨数上都很重要，但在每种情况下起着根本不同的作用。在正常分量的预算中，速度-压力梯度相关项被分解为再分配项和各向同性项，其中再分配项起到在雷诺应力分量之间重新分配能量的作用，各向同性项是湍流动能的压力膨胀源项。在较高的卡洛维茨数下，各向同性项可以忽略不计，再分配项起到各向同性的作用，就像在无反应流动中一样。相反，在低卡洛维茨数时，各向同性项充当一个大的源，而再分配项优先向火焰法向分量注入能量，而牺牲了使湍流不那么各向同性的其他分量。在剪切分量的预算中，在高Karlovitz数时，剪切生产项占主导地位，而在低Karlovitz数时，速度-压力梯度关联项则相反。在低卡洛维茨数下，速度-压力梯度关联项的优势主要是由火焰产生的平均压力梯度引起的，最终导致剪切分量的反Boussinesq行为。总体分析表明，任何依赖于小尺度各向同性和/或快速各向同性的湍流模式都不能很好地反映低卡洛维茨数下湍流的热释放效应。(C)2020年，燃烧研究所。爱思唯尔公司出版，版权所有。
In turbulent premixed flames at low Karlovitz number, combustion heat release can have a significant impact on turbulence. Thermal expansion in flame induces dilatation, and the corresponding pressure-dilatation correlation acts as a primary source of turbulent kinetic energy (TKE). As a consequence, the flame-normal component of the normal Reynolds stresses significantly increases. Additionally, for sheared flames, typical of jet flames, the shear component of the Reynolds stresses exhibits counter-Boussinesq behavior. For flames at low Karlovitz number, where these effects dominate, no models have successfully predicted all Reynolds stress components. To develop more complete turbulence models, heat release effects on the evolution of all Reynolds stress components need to be analyzed. In this work, Reynolds stress budgets are evaluated from Direct Numerical Simulation (DNS) databases of spatially-evolving turbulent premixed planar jet flames at low and high Karlovitz numbers. In the Reynolds stress budgets, the velocity-pressure gradient correlation term is important at both Karlovitz numbers but serves fundamentally different roles in each case. In the budgets for the normal components, the velocity-pressure gradient correlation term is decomposed into a redistribution term and an isotropic term, where the redistribution term acts to redistribute energy between the Reynolds stress components and the isotropic term is the pressure-dilatation source term of turbulent kinetic energy. At high Karlovitz number, the isotropic term is negligible, and the redistribution term acts to isotropize the turbulence as in non-reacting flows. Conversely, at low Karlovitz number, the isotropic term acts as a large source, and the redistribution term preferentially injects energy into the flame-normal component at the expense of other components which acts to make the turbulence less isotropic. In the budget for the shear component, the shear production term dominates the velocity-pressure gradient correlation term at high Karlovitz number, but the opposite is observed at low Karlovitz number. The dominance of the velocity-pressure gradient correlation term at low Karlovitz number is primarily induced by the flame-generated mean pressure gradient and ultimately leads to the counter-Boussinesq behavior of the shear component. The overall analysis indicates that any turbulence model that relies on small-scale isotropy and/or rapid isotropization will fail to capture the heat release effects on turbulence at low Karlovitz number. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.