LES On Lean Premixed Swirl Combustion And Model Comparison

The lean premixed combustion technology not only improves the combustion efficiency of the combustion chamber,but also effectively reduces NOx emissions.In practical applications,it is found that the combustion process is prone to instability such as tempering and thermoacoustic oscillation,which is a major bottleneck hindering the development of the technology.Therefore,based on the macroscopic flame morphology,developing the research of the combustion characteristics of lean-burning swirl in the turbulent environment has meaningful guiding significance for the study of the mechanism of combustion instability.Therefore,this paper focuses on the lean premixed combustion,and conducts experimental research on different flame morphological changes,different flow field conditions and interactions,and builds a Large Eddy Simulation model for lean premixed swirl combustor based on the experiment.Large eddy simulation numerical model focuses on the analysis of the applicable properties of different thermal boundary conditions and sub-grid combustion models and verifies it.Compared with experiments,the large eddy simulation method can predict complex flow field structure,dynamic combustion process and turbulent vortex structure in turbulent premixed combustion.The specific research contents include the following items:(1)The flame morphology of different swirl numbers and equivalence ratios was taken by OH~*Chemiluminescence imaging system.The results show that as the equivalence ratio decreases,the flame undergoes a transition from a compact flame to an M-type flame,and the critical swirl number is critical.The transitional flame occurs in the equivalence ratio of around0.7,and the OH*at the transient flame nozzle exhibits a large irregular oscillation.(2)Using the PIV and OH~*Chemiluminescence to analyze the influence of the compact,M-type and its transition state flow field structure on the combustion process,and provide experimental basis for the establishment of numerical model.Reconstruction of the three-dimensional vortex flow field by the intrinsic orthogonal decomposition method(POD)reveals that PVC dominates the transitional flame flow field and is an important factor for unstable combustion.(3)The effects of compaction,M-type and transition state flow field structures on the combustion process were analyzed by using PIV and OH*self-luminous simultaneous shooting,and experimental basis for numerical model establishment was provided.Reconstruction of the three-dimensional vortex flow field by the intrinsic orthogonal decomposition method(POD)reveals that PVC plays a leading role in the transition flame flow field and is an important factor for unstable combustion.(4)Compared with experiments,large eddy simulation has been able to accurately predict the cold flow field structure.In order to investigate the influence of thermal boundary conditions on the flame structure and flow field prediction accuracy,the two thermal boundary conditions of constant wall temperature and adiabatic are applied to the large eddy simulation calculation of lean burn premixed combustion.By comparing with experimental data,it is found that the adiabatic wall surface obtains more accurate flame structure and flow field velocity and pulsation velocity with respect to the wall temperature.(5)In order to verify the applicability of different combustion models for describing the swirling combustion flow field of complex structures,the two subgrid combustion models were used to simulate the large-eddy simulation of the swirl premixed flame in the combustion chamber.Experiment and simulation The results of comparative analysis show that the calculations agree well with the experimental results,and the flow field structures predicted by the two models are similar.However,the predicted temperature of the FR/ED model is obviously higher,and the TF model is better.The TF model obtains the distribution of velocity,temperature which is more consistent with the experimental data,and the simulation accuracy of the swirl premixed combustion is improved.