Development of large eddy simulation for turbulent combustion flows

本研究旨在发展湍流燃烧流动的大涡模拟(LES)，以用于能源工厂或燃气轮机燃烧室的先进设计。基于时均湍流模拟中发展的火焰面假设，发展了适用于各种湍流火焰和复合燃烧流动的大涡模拟方法及其亚网格尺度(SGS)模型。在湍流火焰模型中引入了动态SGS模型。作为实际应用，在上述大涡模拟的基础上，研究了湍流火焰中NO生成量的预测方法和喷雾燃料的燃烧模型。针对实际的大涡模拟燃烧流动，发展了基于有限差分和有限元的复杂几何形状的湍流模型及其数值方法。提出了标量输运的非平衡SGS模型、壁面边界层近似与时间平均湍流模型相结合以及射流进口速度脉动的数值处理等新结果。由于湍流燃烧流动中的瞬时结构和非定常标量输运现象的报道很少，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动。利用直接数值模拟数据库对小尺度涡旋结构的动力学和相互作用进行了研究。在此基础上，针对扩散火焰无预报、柴油机缸内燃烧器升力火焰预报、先进燃气轮机多级燃烧室预混火焰传播等实际问题，编制了计算机程序。

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.