Development of large eddy simulation for turbulent combustion flows

本研究旨在发展紊流燃烧的大涡模拟（LES），为发电厂或燃气轮机燃烧器的先进设计提供参考。基于时间平均湍流模型中提出的小火焰假设，针对不同类型的湍流火焰和组合燃烧流，建立了LES方法及其子网格尺度（SGS）模型。在紊流火焰模型中引入了动态SGS模型。在实际应用中，基于上述LES模型研究了湍流火焰中NO生成的预测方法和喷雾燃料的燃烧模型。针对实际燃烧流场，建立了基于复杂几何结构的有限差分和有限元的湍流模型及其数值计算方法。本文报道了一些新的结果，提出了标量输运的非平衡SGS模型、结合时间平均湍流模型的壁面边界层近似和射流入口速度波动的数值处理。由于湍流燃烧流中瞬时结构和非定常标量输运现象的研究很少，因此发展了先进的可视化方法，并将其应用于基本燃烧器流中。利用直接数值模拟数据库研究了小尺度涡结构的动力学和相互作用。在上述研究的基础上，对扩散火焰中NO的预测、燃烧燃烧器抬升火焰在柴油机缸内的流动预测、先进燃气轮机多级燃烧室中预混火焰的传播等实际问题进行了计算机程序的研究。

This research aimed a development of large eddy simulation (LES) for turbulent combustion flows for the advanced design of combustors of energy plants or gas turbines. Based on the flamelet assumption which was developed in time-averaged turbulence modeling, LES methods and their subgrid scale (SGS) model are developed for various types of turbulence flames and the combined combustion flows. A dynamic SGS model is introduced into the turbulent flame models. As practical applications, prediction method for NO production in turbulent flames and combustion model of spray fuels are investigated based on the above LES modeling. For the practical LES of combustion flows, turbulence models and their numerical methods are developed based on the finite difference and finite element for the complex geometry. Some new results are reported with proposals of non-equilibrium SGS model for scalar transport, wall boundary layer approximation combined with the time-average turbulence models and numerical treatment of inlet velocity fluctuations in jet flows. Since very few cases were reported on instantaneous structures and unsteady scalar transport phenomena in turbulence combustion flows, advanced visualization methods are developed and applied to the basic burner flows. Dynamics and interaction of small scale eddy structures are also investigated using the database of direct numerical simulation. A computer code based on the above researches is probed on the practical problems, as NO prediction in diffusion flame, lift-up flame of combustion burner flow prediction in diesel engine cylinder, and premixed flame propagation in multi-stage combustor of advanced gas turbine.