The performance of a rather large-scale self-exciting coaxial three-stream airblast injector was studied experimentally and computationally by Strasser (International Journal of Multiphase Flow, 2010). Changes in the relative flow of the inner gas stream produced measurable responses in transient behavior and spray pattern. Particularly, above an inner gas momentum ratio of about 0.2, a transition occurred from a repeatable bursting pattern to one that exhibited a wide range of bursting events. In addition, the spray pattern shifted from unimodal to polymodal. Frequency domain analyses revealed distinct changes in the inner and outer air stream pulsations as a function of air feed rates. Since that work, efforts have progressed in studying the effects of injector geometry on spray characteristics and pulsating flow field response. Geometric features considered included inner nozzle retraction, stream meeting angle, outer annulus gap, and nozzle diameters. Changes to retraction produced the most profound, but not always monotonic, responses in the energy content and nature of the spray pattern. A flushed design was shown to have the strongest pressure pulsations, as well as having the spray bursts moved the farthest downstream of the injector, but only when the angle was moderate. Increases in the other geometric values also moved the ligament formation downstream and reduced the pre-filming dominant frequencies. In general, the time-averaged spray profiles were trimodal in shape and were focused or diffused by geometric permutations. The frequency responses of ligament production and feed pressures did not necessarily coincide; however, all but the highest retraction case exhibited frequencies that were multiples of approximatelv 200 Hz.
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