Pulsating slurry atomization, film thickness, and azimuthal instabilities

A detailed numerical study on a transonic self-sustaining pulsatile three-stream coaxial airblast injector provided new insight on turbulent pulsations that affected atomization. Unique to this investigation, slurry viscosity, slurry annular thickness, and how the annular thickness interacts with inner nozzle retraction (prefilming distance) were found to be paramount to atomizer performance. Narrower annular slurry passageways yielded a thinner slurry sheet and increased injector throughput, but the resulting droplets were unexpectedly larger. As anticipated, a lower slurry viscosity resulted in smaller droplets. Both the incremental impact of viscosity and the computed slurry droplet length scale matched open literature values. The use of a partial azimuthal model produced a circumferentially periodic outer sheath of pulsing spray ligaments, whereas modeling the full domain showed a highly randomized and broken outer band of ligaments. However, quantitatively the results between the two azimuthal constructs were similar, especially farther from the injector; therefore, it was proved that modeling a wedge with periodic circumferential boundaries can be used for screening exercises. Additionally, velocity point correlations revealed that an inertial subrange was difficult to find in any of the model permutations and that droplet length scales correlated with radial velocities. Lastly, droplet size and turbulence scale predictions for two literature cases were presented for the first time using computational fluid dynamics.