Characterization of viscous, non-Newtonian atomization by means of internal waves is presented for a twin-fluid injector. Atomization of such fluids is challenging, especially at low gas-liquid mass ratios (GLRs). This paper details mechanisms that enhance their disintegration in a "wave-augmented atomization" process. The working fluid, banana puree, is shear-thinning and described by the Herschel-Bulkley model. Unlike a conventional airblast injector, an annular flow of banana puree is injected into a core steam flow, encouraging regular puree waves to form inside the nozzle. A pulsing flow develops with three distinct stages: stretch, bulge, and burst leading to an annular puree sheet stretching down from the nozzle exit. Rayleigh-Taylor instabilities and viscosity gradients destabilize the surface. During wave collapse, the puree sheet bulges radially outward and ruptures violently in a radial burst. Near-nozzle dynamics propagate axially as periodic fluctuations in Sauter mean diameter occur in a wave pattern. Numerical simulations reveal three atomization mechanisms that are a direct result of wave formation: 1) wave impact momentum, 2) pressure buildup, and 3) droplet breakaway. The first two are the forces that exploit puree sheet irregularities to drive rupture. The third occurs as rising waves penetrate the central steam flow; steam shear strips droplets off, and more droplets break away as the wave collapses and partially disintegrates. Waves collapse into the puree sheet with a radial momentum flux of 1.7 × 105 kg/m-s2, and wave-induced pressure buildup creates a large pressure gradient across the puree sheet prior to bursting.

We reveal mechanisms driving pre-filming wave formation of non-Newtonian banana puree inside a twin-fluid atomizer at a steam-puree mass ratio of 2.7%. Waves with a high blockage ratio form periodically at a frequency of 1000 Hz, where the collapse of one wave corresponds to the formation of another (i.e., no wave train). Wave formation and collapse occur at very regular intervals, while instabilities result in distinctly unique waves each cycle. The average wave angle and wavelength are 50{degree sign} and 0.7 nozzle diameters, respectively. Kelvin-Helmholtz instability (KHI) dominates during wave formation, while pressure effects dominate during wave collapse. Annular injection of the puree into the steam channel provides a wave pool, allowing KHI to deform the surface; then, steam shear and acceleration from decreased flow area lift the newly formed wave. The onset of flow separation appears to occur as the waves' rounded geometry transitions to a more pointed shape. Steam compression caused by wave sheltering increases pressure and temperature on the windward side of the wave, forcing both pressure and temperature to cycle with wave frequency. Wave growth peaks at the nozzle exit, at which point the pressure build-up overcomes inertia and surface tension to collapse and disintegrate the wave. Truncation of wave life by pressure build-up and shear-induced puree viscosity reduction is a prominent feature of the system, and steam turbulence does not contribute significantly to wave formation. The wave birth-death process creates bulk system pulsation, which in turn affects wave formation.

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