An Application of LES for Gas Turbine Combustor

A three-dimensional turbulence spray combustion simulation in a gas turbine combustor with Large Eddy Simulation is carried out. In this study, we construct a new eddy characteristic time model derived from a large-scale motion to estimate the combustion reaction rate with an eddy dissipation concept (EDC) model, and estimate combustion characteristics (temperature and chemical species distribution) in the gas turbine combustor for the purpose of validating this model. The essence of this model is that eddy characteristic time is estimated by considering Kolmogorov scale at first. From this assumption, eddy dissipation rate is apparent. However it is not solved directly in Large Eddy Simulation. So eddy dissipation rate is estimated by an assumption that turbulence energy generation and dissipation are locally equal (it is the same assumption as Smagorinsky model), and it is substituted in the eddy characteristic time formula. The overall reaction C₁₂H₂₄+18O₂ → 12CO₂+12H₂O, is often used for turbulent combustion simulation for saving calculation time, but cannot consider CO and H₂ formation in local fuel-rich region. To solve this problem, we use 3-step global mechanism (C₁₂H₂₄+6O₂ → 12CO+12H₂, CO+0.5O₂ ↔ CO₂, H₂+0.5O₂ ↔ H₂O) to calculate turbulent non-premixed flame characteristics coupling with EDC. The calculated CO₂ mole fraction distribution is in fairly good agreement with the experimental data. However, the calculated temperature distribution does not agree well with the measured result of temperature because of disturbing heat transport to downstream by dilution air jet. Though few problems are left, it is shown that the combustion simulation using LES with EDC model is effective method to calculate the characteristics of turbulent diffusion flame in furnace such as gas turbine combustor.