Direct Numerical Simulation Of Triple Flame Based On Detailed Reaction Mechanism And REDIM Method

In the actual dynamic combustor,the combustion process is often accompanied by premixed combustion and non-premixed combustion.Triple flame,as a unique partially premixed flame,plays an important role in the flame propagation of partially premixed systems,and is of great significance for understanding the stability of lifting diffusion flame.However,for some partially premixed flames,there are some limitations in the use of a few-step chemical reaction mechanism or single-regime flamelet models in the numerical simulation.Therefore,it is of theoretical and practical significance to study the fundamental characteristics and chemical simplification methods of triple flame under different conditions.In this paper,the direct reaction simulation(DNS)of triple flames under different concentration gradients was carried out using a detailed reaction mechanism.At the same time,the reaction-diffusion manifold(REDIM)method was used to generate a suitable 2D REDIM lookup table,which was implanted into the lesocc2 c program for DNS calculation of the triple flame,and compared with the results of the detailed chemical reaction mechanism.To verify the performance of the 2D REDIM table.Firstly,DNS calculation of triple flame was carried out by detailed mechanism.Six cases of inlet width of 5 mm,10 mm,15 mm,20 mm,25 mm and 30 mm,respectively,were calculated under the condition that the range of equivalent ratio of mixture stayed the same.The results show that as the width increases(the concentration gradient decreases),the thickness of the triple flame gradually increases and the premixed flame branches become longer.At the same time,the OH mass fraction of the triple point and premixed branches gradually increased,while the OH mass fraction at the branch of the diffusion flame gradually decreased.Since the range of the equivalent ratio of the inlet mixture remains unchanged,the premixed flame thickness hardly changes with the width.Moreover,the flame velocity of the triple point has a maximum value in the concentration gradient.Then,DNS calculation of triple flame has benn carried out by six-step reaction mechanism,28-step reaction mechanism and 2D REDIM table.It is found that,the sixstep mechanism can capture the three branches of the triple flame;however,the temperature and component field are quite separated from the results of detailed mechanism.Indicating that it is difficult to describe the triple flame structure with very few chemical reaction mechanisms.The temperature and main components predicted by 28-step mechanism and 2D REDIM table are almost identical with the detailed mechanism.The results of some intermediate components deviate from the detailed mechanism,but the 2D REDIM table results are better than the 28-step reaction mechanism.At the same time,compared with the detailed mechanism and 28-step mechanism,the use of 2D REDIM table greatly reduces the amount of calculation,which further shows that the 2D REDIM table can be well applied to partial premixed combustion.