Kashdan, Julian T. and Shrimpton, John S.
Characteristics of transient, swirl-generated, hollow-cone sprays
Atomization and Sprays, 16, (5), . (doi:10.1615/AtomizSpr.v16.i5.20).
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The near-nozzle, global, spatial, and temporal characteristics of a hollow-cone spray produced by a pressure swirl-type atomizer have been investigated experimentally. Particular attention is given to the transient phase just after needle opening, which, for pulsed or intermittent atomizers, plays an all-important role in defining the global spray behavior and, more significantly, atomization quality. Qualitative and quantitative spray measurements have been achieved via the combined diagnostic techniques of high-magnification charge-coupled device (CCD) imaging and phase Doppler anemometry (PDA), which provides useful data not only in terms of improving the design and performance of pressure swirl atomizers, but also for the validation and refinement of numerical spray models. High-magnification CCD images of the intact near-nozzle liquid sheet reveal a certain degree of helical swirl motion, although laser Doppler velocimetry (LDV) results indicate that the tangential swirl motion imparted on the liquid sheet decays rapidly within the first few millimeters of the atomizer orifice to near-negligible levels. Images of the poorly atomized “preswirl spray” formed during the early transient phase of injection also revealed the presence of large, nonspherical liquid masses up to 1 mm in size, even as far as 72 nozzle diameters downstream. The spray-induced gas phase flow, which results in the characteristic toroidal vortex, was found to have a significant influence on droplet trajectories and segregation of the fast-moving large (D32 between 25 and 30 ?m) and small (1?5 ?m) droplets within the spray. Estimates of characteristic droplet Weber numbers have also been made, which, in general, were found to be less than the critical values required for secondary droplet breakup to occur.
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