An Analytical-Empirical Approach to Model Liquid Fuel Combustion Dynamics

Combustion dynamics is one of the most important factors to be understood and navigated in the design of modern gas turbine combustors. For liquid-fueled combustors this becomes especially challenging given the complexity of additional physics involved, which includes fuel atomization and transport, mixing, reactive kinetics, and acoustics. In this paper an analytical approach to model combustion dynamics is described for an industrially relevant liquid fuel nozzle. For determining the flame fluctuating heat release response to inflow perturbations, an analytical liquid-fuel model was leveraged, developed as an extension and augmentation of traditional diffusion flame models. The acoustic response of the combustor was calculated using 3D finite-element models, including acoustic damping effects of key geometric features. These individual responses were then utilized in a time-domain Green’s function based approach to calculate the response, including growth and saturation, of pressure oscillations. To gain modeling approach confidence and enhanced accuracy, some model parameters impacted by real effects were calibrated manually to achieve better general agreement with the breadth of experimental and computational data available. This included measured flame transfer functions and dynamics metrics, both frequencies and amplitudes, and computed mode shapes and flame shapes. The calibrated modeling approach was then applied to two different combustors, a single-cup and full-annular configurations. It was found that the results agreed well with test data, especially trend-wise, across a modest range of operating conditions. However, at conditions which extended too far beyond the bounds of the data used for model calibration, model inaccuracies became evident. Lastly, sources of model inaccuracies and areas for improvement were discussed.