Modeling partially premixed combustion behavior in multiphase LES

A partially premixed flamelet model is extended to account for liquid fuel, and its accuracy and dependence on spray modeling inputs are investigated. The spray and combustion model coupling is considered by simulating single drop evaporation experiments. These simulations confirmed previous findings showing that small changes in spray model assumptions significantly influence evaporation rates. The analysis is then extended to Large Eddy Simulation (LES) using a NASA model aircraft combustor burning Jet-A fuel. Results indicate the partially premixed flamelet approach can describe the range of combustion physics found in the burner. However, they also reveal that the liquid model sensitivities hold in LES, where a tight coupling exists between combustion model predictions and spray model assumptions. Details of the liquid modeling approach, including thermodynamic specifications and descriptions of liquid spray at the nozzle outlet, influence the burning regime, mean gas temperatures, and emissions levels predicted by LES. The results suggest that while the combustion model is capable, spray model influences must be firmly understood before validation can be accomplished in liquid fueled contexts.