Numerical Study Of Fuel/Air Unmixedness In A Nonreacting Gas Turbine Combustor

Gas turbine is widely used in power engineering because of high efficiency and low emissions, and how to decrease the NOx emissions in gas turbine and combined cycle has received considerable attention recently. The combustor is the most important element to control the emissions. Recently, Dry Low NOx (DLN) combustor is an important object for investigation. The ability of a lean-premixed combustion system to minimize NOx emissions relies upon how well the fuel and air is premixed. Based on the topic, the flow field in the premixer of a gas turbine is simulated, in order to evaluate fuel/air unmixedness at different fluid conditions.In this thesis, the mathematical models for turbulent diffusion are developed based on the characteristics of the diffusion. The k -εturbulence two equation model is applied to predict the real flow, while scalar transport model is used to describe the mass transfer in fluid systems. The finite volume method is used to discretize differential equations. It is found that the simulated results agree well with experiments.Fuel/air unmixedness is evaluated at different fluid conditions. The effect of the length of the premixer on fuel/air unmixedness is studied, along with other variables including the average velocity of the mixture, turbulent intensities, the ratio between the momentum of fuel and air, stoichiometric ratio, temperature, pressure, swirl number as well as the number of the jets. A general formula is developed to predict fuel/air unmixedness based on the results of this paper. Several ways to improve the performance of the premixer is discussed.Flow field and mass transfer in the cooling part of a gas turbine combustor are simulated. Simulated results are compared with experiments'. With the conclusion which is generated in the former part, the effect of the turbulent intensities on nonuniformity of the temperature field is studied, as well as the ratio between the momentum of fuel and air on the depth that the cooling air has penetrated. The results of simulation provide the reference for the DLN combustion technique and the design for advanced gas turbine combustor.