Subgrid-scale models and large-eddy simulation of oxygen stream disintegration and mixing with a hydrogen or helium stream at supercritical pressure
Subgrid-scale models and large-eddy simulation of oxygen stream disintegration and mixing with a hydrogen or helium stream at supercritical pressure
复制标题
超临界压力下氧气流分解和与氢气或氦流混合的亚网格尺度模型和大涡模拟
DOI：
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发表时间：
2011
影响因子：
3.7
通讯作者：
J. Bellan
中科院分区：
文献类型：
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作者：
E. Taşkinoğlu;J. Bellan
对于超临界压力 p 下的流动，大涡模拟 (LES) 方程由微分守恒方程和真实气体状态方程组成，并且方程利用取决于热力学变量的输运特性。与之前的 LES 模型相比，微分方程不仅包含次网格尺度 (SGS) 通量，还包含新的 SGS 项，每个项都表示为“校正”。这些附加项通常假设大气压流为空，源自对微分控制方程的过滤，并且表示过滤项与作为过滤流场的函数计算的相同项之间的差异（除了对流项贡献之外）。特别是，能量方程包含热通量校正（q 校正），它是分子热通量的滤波发散度与作为滤波流场的函数计算的分子热通量发散度之间的差值。我们在此回顾之前的一项先验研究，其中我们在 q 校正项建模方面仅取得了部分成功，并表明使用不同的建模方法可以取得成功。基于时间混合层直接数值模拟数据库的先验分析表明，q 校正建模的重点应该是重建原始变量梯度而不是它们的系数，并提出近似反卷积模型（ADM）作为 LES 分子热通量计算流场重建的有效手段。此外，还对最初在下游含有氧 (O) 和在上游含有氢 (H) 或氦 (He) 的时间混合层进行了事后研究，以检验新模型的优势。结果表明，对于任何包括 SGS 通量模型（恒定系数梯度或尺度相似模型；动态系数 Smagorinsky/Yoshizawa 或混合 Smagorinsky/Yoshizawa/梯度模型）的 LES，在 LES 中包含 q 校正会导致 SGS 分子热通量差异在理论上得到最大程度的减小；因此，对这个新的子网格项进行建模时剩余的误差是不可减少的。还证明了 q 校正模型首先对分子热通量的影响，然后对因变量的均值、波动、二阶相关性和空间分布的影响。讨论了模型在一般 LES 中的应用。
For flows at supercritical pressure, p, the large-eddy simulation (LES) equations consist of the differential conservation equations coupled with a real-gas equation of state, and the equations utilize transport properties depending on the thermodynamic variables. Compared to previous LES models, the differential equations contain not only the subgrid-scale (SGS) fluxes but also new SGS terms, each denoted as a ‘correction’. These additional terms, typically assumed null for atmospheric pressure flows, stem from filtering the differential governing equations and represent differences, other than contributed by the convection terms, between a filtered term and the same term computed as a function of the filtered flow field. In particular, the energy equation contains a heat-flux correction (q-correction) which is the difference between the filtered divergence of the molecular heat flux and the divergence of the molecular heat flux computed as a function of the filtered flow field. We revisit here a previous a priori study where we only had partial success in modelling the q-correction term and show that success can be achieved using a different modelling approach. This a priori analysis, based on a temporal mixing-layer direct numerical simulation database, shows that the focus in modelling the q-correction should be on reconstructing the primitive variable gradients rather than their coefficients, and proposes the approximate deconvolution model (ADM) as an effective means of flow field reconstruction for LES molecular heat-flux calculation. Furthermore, an a posteriori study is conducted for temporal mixing layers initially containing oxygen (O) in the lower stream and hydrogen (H) or helium (He) in the upper stream to examine the benefit of the new model. Results show that for any LES including SGS-flux models (constant-coefficient gradient or scale-similarity models; dynamic-coefficient Smagorinsky/Yoshizawa or mixed Smagorinsky/Yoshizawa/gradient models), the inclusion of the q-correction in LES leads to the theoretical maximum reduction of the SGS molecular heat-flux difference; the remaining error in modelling this new subgrid term is thus irreducible. The impact of the q-correction model first on the molecular heat flux and then on the mean, fluctuations, second-order correlations and spatial distribution of dependent variables is also demonstrated. Discussions on the utilization of the models in general LES are presented.