Banana Puree Wave Cycle in Twin-Fluid Atomizer

We present a numerical study of annular wave cycling inside a novel twin-fluid injector. Such waves provide mechanisms to enhance the atomization of viscous, non-Newtonian fluids. The working fluid is banana puree, which is both shear- and temperature-thinning and flows in an outer annulus surrounding a high-speed steam flow. The steam-puree mass ratio is 2.7%. As the puree is injected into the central steam flow, periodic waves cycle at a frequency of 1000 Hz. No wave train exits; rather, a new wave is birthed in the wake of a dying wave. Waves on average have a wave angle of 50° and a wavelength of 0.7 nozzle diameters. The Kelvin-Helmholtz instability (KHI) deforms the puree surface and dominates the wave formation process. Waves are characterized by a high blockage ratio, causing significant windward pressure buildup and transonic steam flow above the crest. Accelerated steam provides a lifting force, but pressure eventually overcomes inertia and surface tension at the nozzle exit, resulting in wave collapse and rupture. As the steam compresses and decompresses during wave formation and collapse, pressure, temperature, and velocity cycle with wave frequency. The result is bulk system pulsation, which provides feedback that influences wave cycling.