Which Way Do We Go? Self-Induced Axis-Switching Periodic Swirl in Annular Liquid Sheets

The aim is to characterize the mechanism for self-induced swirl-switching in flow through a steam-assisted transonic pulsing banana puree heater/atomizer. As the cold puree and hot steam interact, a cycle of blockage and release occurs; deformation of the non-Newtonian puree produces a wave which impedes the motion of the steam. This results in an increase in heat and pressure until the buildup of steam exceeds the banana puree’s ability to contain its motion. At this point the steam is able to force through the puree, producing more deformation and propagating the cycle. Augmenting the cycle are the traditional Kelvin-Helmholtz instabilities (KHI) for streamwise disturbance amplification and Rayleigh–Tayler instabilities (RTI) for azimuthal amplification. However, what was revealed is an additional feature of the flow never before identified. The high blockage ratio of the steam, due to the thick deforming annular puree sheet, encourages fin-like puree protrusions into the steam. Once formed, both sides of these protrusions begin to exhibit KHI and RTI in a plane orthogonal to the original perturbations. The result is a periodic axis-switching in which the self-induced puree swirl spontaneously alternates in both directions.