A Unified Manifold-Based Approach to Modeling Turbulent Combustion

开发新型高效低排放燃烧系统的主要障碍之一是缺乏可靠的、可负担的、预测的计算模型来描述湍流燃烧。发展这种模型的主要挑战是描述燃烧过程和湍流之间的关系。虽然已经开发了广泛的模型来描述湍流对燃烧过程的影响，但没有通用的模型来描述燃烧过程对湍流的影响。目前的湍流模型隐含地假设燃烧热释放对湍流没有影响，这一事实与观测结果相反。该项目将开发一种新的建模方法，能够捕捉燃烧过程和湍流之间的双向耦合。在新的方法中，有关燃烧过程的信息直接嵌入到湍流模型中。新模型将根据一组实验室规模湍流燃烧的计算数据库和实验数据库进行评估。随着燃烧过程和湍流之间的双向耦合被完全捕获，新的建模方法将能够真正预测湍流燃烧的模拟，促进新的清洁燃烧系统的发展。新建模方法的软件实现也将公开提供给其他研究人员和工业界使用。尽管已知燃烧热释放对湍流的影响，特别是反梯度输运现象，但反应流中的湍流模型通常改编自非反应流群落，隐含地假设燃烧热释放对湍流没有影响。该项目将为湍流燃烧的大涡模拟（LES）开发一种全新的方法，该方法将考虑湍流和燃烧之间的完全耦合相互作用。该方法不仅依赖于热化学标量方程的条件滤波，而且依赖于一个或多个火焰结构变量的动量方程的条件滤波。该方法将湍流模型与火焰动力学模型分离，将火焰动力学模型嵌入到条件滤波中，简化了闭包模型。在推导有条件过滤的控制方程并使用直接数值模拟（DNS）的数据分析其预算之后，将使用基于物理的方法和基于数据的方法相结合来开发封闭模型。最终，统一的基于流形的方法将实现到一个计算工具中，针对当前的建模方法进行基准测试，并针对湍流预混和分层火焰的实验测量进行验证。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the major impediments to the development of new high-efficiency low-emissions combustion systems is the lack of reliable, affordable, predictive computational models for describing turbulent combustion. The primary challenge in developing such models is describing the relationship between combustion processes and turbulence. While a broad range of models have been developed for describing the effects of turbulence on combustion processes, no general models exist for describing the effects of combustion processes on turbulence. Current turbulence models implicitly assume that combustion heat release has no effect on turbulence, a fact contrary to observation. This project will develop a new modeling approach capable of capturing the two-way coupling between combustion processes and turbulence. In the new approach, information about the combustion processes is directly embedded into the turbulence model. The new model will be evaluated against a set of computational databases and experimental databases of laboratory-scale turbulent combustion. With the two-way coupling between combustion processes and turbulence fully captured, the new modeling approach will enable truly predictive simulations of turbulent combustion, facilitating the development of new clean combustion systems. The software implementation of the new modeling approach will also be made publicly available for use by other researchers and in industry.Despite the known influences of combustion heat release on turbulence, notably the phenomenon of counter-gradient-transport, turbulence models in reacting flows are usually adapted from the non-reacting flow community, implicitly assuming no effect of combustion heat release on turbulence. This project will develop a fundamentally new approach for Large Eddy Simulation (LES) of turbulent combustion that accounts for fully coupled interactions between turbulence and combustion. The approach relies on the conditional filtering of not only the thermochemical scalar equations but also the momentum equation with respect to one or more flame structure variables. With this approach, the modeling of turbulence is divorced from the flame dynamics, which are embedded into the conditional filtering, and simplifies closure modeling. After deriving the conditionally filtered governing equations and analyzing their budgets using data from Direct Numerical Simulation (DNS), closure models will be developed using a combination of physics-based approaches and data-based approaches. Ultimately, the unified manifold-based approach will be implemented into a computational tool, benchmarked against current modeling approaches, and validated against experimental measurements of turbulent premixed and stratified flames.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.