Numerical study of a swirl atomized spray response to acoustic perturbations

A numerical study of the spray evaporation response to acoustic perturbations is presented. Thermoacoustic instabilities are the result of a resonant loop between the acoustic pressure waves in the form of velocity fluctuations and the heat release of the combustion phenomena. Premixed flame instability can be relatively simply characterized through the flame transfer function (FTF). In the case of non-premixed and partially premixed spray flames, the droplet atomization and subsequent evaporation is known to be related to the heat release rate of the combusting flame and have an effect on the resulting FTF. This paper examines the interaction between the acoustic field perturbation and the droplet evaporation by means of a numerical simulation of a pressurized Airblast type swirl atomizer. The fuel droplets are introduced into the computational domain of the burner at the location of film release and break up in a simplified droplet injection model. The resulting Eulerian-Lagrangian fuel spray simulation is used to represent the spray evolution after fuel film breakup within the shear region of the swirl atomizer. The droplet evolution is studied in the downstream region. In contrast with observations in other burners, in this specific burner design, the evaporation phenomena do not respond significantly to the high frequency velocity forcing. The interplay between the slip velocity perturbations and the vaporization rate is shown to have a complicated dependency on forcing amplitude in swirl atomizers