Investigation of initial droplet distribution and importance of secondary breakup model on lean blowout predictions of a model gas turbine combustor

In the present work, the importance of secondary droplet breakup and the impact of the initial droplet distribution on lean blowout (LBO) predictions is investigated to determine the sensitivity and robustness of the prediction to spray boundary conditions and secondary breakup models, respectively. This is accomplished using large-eddy simulations of a model gas turbine combustor, operating near the LBO limit. The flow field and gas phase chemistry is solved using an unstructured Navier-Stokes solver and a flamelet/progress variable formulation, respectively. Liquid spray is modeled using a polydisperse droplet injection and a Lagrangian spray evaporation model. Simulations with and without stochastic modeling of droplet breakup are performed. An analysis of the droplet Weber number indicates that large diameter droplets are above the critical Weber number and should undergo secondary breakup. The present study demonstrates that secondary droplet breakup has a significant impact on the predicted droplet distribution and temporal evolution of the flame. Due to the large computational requirements of the current simulations, an ad-hoc approach to determining the initial droplet SMD and diameter is not feasible and a secondary droplet breakup model is required to reproduce the experimental trends.