Application of a Partially Premixed Laminar Flamelet Model to a Low Emissions Gas Turbine Combustor

Abstract

Computational combustion dynamics simulations have been used widely for the design and analysis of conventional rich dome combustors using a fast chemistry assumed shape PDF approach (Shyy et al. 1986) and/or an eddy-breakup model (Valachovic, 1993, Danis et al., 1996). The application of these tools to ultra-low emissions combustors such as the GE LM6000 DLE has been hampered by the inadequacies of the eddy break-up combustion model. In the present work, a partially-premixed laminar flamelet combustion model, based initially on the model of Müller et al. (1994), is applied to an LM6000 single cup combustor. The basic fluid mechanical code is ACC, using the k-ε turbulence model (Prakash, et al., 1998). Assumed-shape PDF models are used for mixture fraction Z(x), and the scalar field G(x), whose level surfaces G = G0 represent the flame location. The model includes the effects of local strain rate on flame propagation rate and extinction through modification of the turbulent flame speed correlation, which determines the rate of propagation of the scalar field variable G. The effects of variable inlet fuel/air ratio variance (unmixedness) on predicted NOx emissions are included through the moments of a calculated NO source term on the PDF’s of Z, and include the contributions of flame-front production of NO in premixed flames. Comparisons to measured velocity and emissions data are shown.