Numerical Simulation Study On Premixing Performance And Combustion Flow Field In Low Emission Combustor

Nowadays,environmental protection laws are becoming more and more strict,which makes the low emission technology of gas turbine becoming more and more important.For the combustor of gas turbine which using natural gas as fuel,the combustor dome,which acts as flame stabilizer and mixer,has significant impact on combustion characteristics.The mixedness uniformity of air and fuel will affect the temperature distribution and thus influence the emissions.The quality of the flow field will directly affect the performance of the combustion field and the pollutant emissions.Hence,it is of great improtance to study the fuel-air premixing laws and design methods of dome.Based on an annular combustor,the numerical simulation method is used to study the fuel-air premixing performance in the combustor dome and the prediction laws are given.Meanwhile,the performance of the flow field is studied and the prediction method is proposed.The research results have important guiding significance for the dome structure design of low emission combustor.The main work of this paper is as follows:(1)For the fuel-air premixing performance of the dome of combustor,the numerical simulation method is used to study the influence of controllable boundary parameters on the premixing performance in the flow passage of a tower swirler.The corresponding qualitative rules and empirical prediction formulas are obtained by changing momentum ratio,inlet air velocity,arrangement of premixing holes,number of holes,diameter of holes and the mixing distance.Results show that the premixing performance can get better by prolonging the mixing distance,and the positions of orifices can have an important influence on mixedness uniformity—put them on both windward side and leeside would make premixing performance meet the demand.When momentum ratio stays a fixed value,increasing the distance between holes properly can improve the uniformity.Premixing performance can also be better by increasing the diameter of orifices after a fixed value.Besides,increasing momentum ratio can not always improve the premixing performance.(2)Basing on an annular combustor,a three-staged tower swirler is designed.This structure can perform very well under the pilot mode and the premix mode,except for total pressure loss.Besides,with reference to the calculating results,the prediction law of premixing performance is improved.(3)For the characteristics of the flow field in the combustor,numerical simulation method is used to study the combustion flow field when changing the swirl number in the range of 0.7-1.3,and a prediction model is established to predict the size parameters of recirculation zone in the hot field through the cold field.It is found that the shape of the recirculation zone in the cold field can determine the basic shape of the combustion temperature field and the reaction zone.With the increase of swirl number,the width and length of the recirculation zone generally increase,and the expansion angle of streamline increases,the recirculation area becomes significantly larger.With the increase of the swirl number,the total pressure loss increases.Besides,the design method of the fuel-air premixing structure in low emission combustor is obtained.