A Priori Analysis of Subgrid Molecular Transport Effects on High Pressure Turbulent Combustion Modeling

该提案解决了与现代柴油机，燃气轮机和火箭发动机相关的现实高压热力学条件下湍流火焰的子网格统计。该研究将利用大规模并行直接数值模拟（DNS），利用高阶精确技术完全解决湍流火焰的所有长度和时间尺度，而不使用湍流或子网格模型，来分析几种高压火焰。重点是分析与现代燃烧模型相关的术语，重点是大涡模拟（LES）和过滤密度函数（FDF）方法。高压实验是困难的，这些方法的现有DNS验证到目前为止还没有解决在真实火焰中非常重要的四个耦合现象：大压力、真实化学、真实属性模型以及广义的热量和质量扩散。知识价值：假设局部亚网格分子混合效应，通常被认为相对于湍流搅拌可以忽略不计，可以对高压火焰动力学产生实质性影响。这是因为最终许多火焰是由物质和温度的扩散局部控制的。熄灭和重燃事件对局部火焰条件高度敏感，Soret交叉扩散在高压下也高度放大。因此，将对氢-氧、氢-空气、庚烷-空气和甲烷-空气反应的剪切层进行DNS。详细和简化的化学动力学，一个真实的气体状态方程，真实的性质评估，和一个完整的广义扩散模型将纳入。大规模并行模拟将为不同压力和雷诺数下的每种火焰生成数据库。然后将以先验的方式对数据库进行探索，以分析与高压湍流燃烧的LES和FDF相关的子网格术语和统计数据。需要建模的术语将被识别并适当建模。更广泛的影响：这项研究有望提高社会预测高压下湍流燃烧的能力。由于社会上使用的碳氢化合物燃烧装置（包括柴油发动机、燃气轮机、火箭发动机和其他潜在的氢技术）的燃烧室压力不断增加，这是势在必行的。研究生和本科生都将参与其中。此外，教育计划的多学科部分包括将参与这项研究的研究生与北卡罗来纳大学夏洛特分校的一组计算机工程师聚集在一起。DNS代码将在UNCC并行FPGA集群上共享和运行。这个练习的目的是：在两个典型的非交叉组之间共享知识，以及为典型和高级并行体系结构优化代码。

Miller0965624This proposal addresses subgrid statistics of turbulent flames under realistic high pressure thermodynamic conditions relevant to modern diesel engines, gas turbines, and rocket engines. The research will utilize massively parallel direct numerical simulations (DNS), in which all length and time scales of the turbulent flame are fully resolved using high order accurate techniques and without the use of turbulence or subgrid models, to analyze several high pressure flames. The particular focus is on analyzing terms relevant to modern combustion models with emphasis on large eddy simulation (LES) and filtered density function (FDF) approaches. High pressure experiments are difficult and existing DNS validations of these approaches have thus far not addressed four coupled phenomena that can be highly important in real flames: large pressure, realistic chemistry, real property models, and generalized heat and mass diffusion.Intellectual Merit: It is hypothesized that localized subgrid molecular mixing effects, which are often assumed to be negligible relative to turbulent stirring, can have a substantial impact on high pressure flame dynamics. This is due to the fact that ultimately many flames are controlled locally by the diffusion of species and temperature. Extinction and re-ignition events are highly sensitive to local flame conditions and Soret cross-diffusion is also highly amplified at high pressures. DNS will therefore be conducted for hydrogen-oxygen, hydrogen-air, heptane-air, and methane-air reacting shear layers. Both detailed and reduced chemical kinetics, a real gas state equation, real property evaluations, and a complete generalized diffusion model will be incorporated. Massively parallel simulations will produce a database for each flame at various pressures and Reynolds numbers. The database will then be explored in an a priori manner to analyze subgrid terms and statistics related to LES and FDF of high pressure turbulent combustion. Terms requiring modeling will be identified and modeled as appropriate.Broader Impact: The research is expected to enhance society's ability to predictively model turbulent combustion at elevated pressures. This is imperative due to the ever increasing combustion chamber pressures encountered in hydrocarbon combustion devices utilized in society (including diesel engines, gas turbines, rocket engines, and other potential hydrogen technologies). Both graduate and undergraduate students will be involved. In addition, a multidisciplinary portion of the education plan involves bringing together the graduate students involved with this research with a group of computer engineers at UNC Charlotte. The DNS code will be shared and run on the UNCC parallel FPGA cluster. The purposes of this exercise are: knowledge sharing between two typically non-intersecting groups, and code optimization for both typical and advanced parallel architectures.