采用k-ε-g湍流模型、23步反应机理和径向平均条件矩封闭(Conditional Moment Closure)CMC技术,模拟了氢气湍流提升火焰结构,并探讨了火焰稳定机理.作为针对湍流提升火焰进行耦合CMC模型的多维大涡模拟LES的第一步,计算考虑了湍流对燃烧的作用,数值格式采用高精度Padé格式,推导并采用了基于特征波分析的多组分条件矩Navier-Stokes特征边界条件NSCBC,本研究暂不考虑热释放对湍流的影响,模拟集中于火焰提升区域.与国际上公布的相关实验数据的比较表明,模型精确地预测了提升高度、Favre径向平均温度和组分浓度.研究结果表明,径向平均CMC模型能够较好重构目前仍争议较大的提升火焰稳定机理.
A kinetic modeling of pollutant formation in hydrocarbon flames is presented through analysis of hierar- chical structures. Based on the newly released GRI-Mech 3.0, it was mainly taken from Dean and Bozzelli (DB) and Wang mechanism respectively for the nitrogen chemistry, the for- mation and growth of polycyclic aromatic hydrocarbons (PAH). The modeling was improved by considering C4 and Howard’s PAH chemistry. The mechanism consists of 121 species in 731 reactions. Two premixed flame structures are predicted, and the computed results are compared with the experimental ones. It is shown that the mechanism predicts reasonably well the concentration profiles of major, key in- termediate and minor species.
Results obtained using conditional moment closure (CMC) approach to modeling a lifted turbulent hy-drogen flame are presented. Predictions are based on k-ε-g turbulent closure, a 23-step chemical mechanism and a ra-dially averaged CMC model. The objectives are to find out how radially averaged CMC can represent a lifted flame and which mechanism of flame stabilization can be described by this modeling method. As a first stage of the study of multi-dimensional CMC for large eddy simulation (LES) of the lifted turbulent flames, the effect of turbulence upon combustion is included, the high-order compact finite- difference scheme (Padé) is used and previously developed characteristic-wave-based boundary conditions for multi- component perfect gas mixtures are here extended to their conditional forms but the heat release due to combustion is not part of the turbulent calculations. Attention is focused to the lift-off region of the flame which is commonly considered as a cold flow. Comparison with published experimental data and the computational results shows that the lift-off height can be accurately determined, and Favre averaged radial profiles of temperature and species mole fractions are also reasonably well predicted. Some of the current flame stabili-zation mechanisms are discussed.
