基于层流小火焰和beta-PDF的预混燃烧模型

研究了基于层流小火焰概念和假定beta-PDF(probability density function)的湍流预混燃烧模型.该模型采用PREMIX程序来计算层流小火焰,将计算结果表示为进程变量的函数,并利用进程变量的beta-PDF积分生成了用于RANS(雷诺平均Navier-Stokes)计算的PDF表.以化学当量的甲烷湍流本生火焰为算例对模型进行了计算验证,并与Zimont模型的计算结果和实验结果做了对比.结果表明,平均速度分布与实验符合的较好,温度和湍动能计算结果有待改善.本模型高估了化学反应速率,导致计算火焰比实际瘦,这是因为模型中未能考虑湍流对火焰的拉伸和弯曲效应,考虑湍流拉伸和弯曲效应的预混燃烧模型是今后进一步研究的方向.

Premixed combustion model based on laminar flamelet and presumed beta-PDF

Based on the laminar flamelet concept and the presumed beta-PDF(probability density function),a turbulent premixed combustion model was studied.In this model,the laminar flamelet calculation was performed with one dimensional free propagation flame code,PREMIX.The results of the laminar flamelet calculation can be formulated as functions of progress variable and then integrated with the presumed beta-PDF,which produced a lookup table.This model was validated with the calculation of the turbulent Bunsen flame for stoichiometric methane.The results were compared with the results of Zimont model and the experiment,which show that the calculation here can appropriately predict the distribution of average velocity.However,the turbulent kinetic energy and temperature are not so well captured and the mean reaction rate is likely overpredicted,which lead to a shorter flame brush.This is likely because of the exclusion of turbulent stretch effect on the flame surface.A model which can account for the effect of turbulent stretch will be explored in future studies.