Internal Flow Physics of a Fluidic Oscillator Spray in the Transition Regime

Abstract

An experimental investigation of the underlying flow physics of a dual-jet interaction fluidic oscillator spray has been conducted in the transition regime for a Reynolds number of 1680. The transition regime is defined as a narrow range of flow rates between two other operating modes of the fluidic oscillator. Particle image velocimetry (PIV) was used with refractive index-matching sodium iodide solution to minimize reflections from the spray geometry and obtain detailed internal velocity fields. PIV results show that the interaction of the two internal jets and the resultant vortices are responsible for the oscillation mechanism in the transition regime. Two side vortices sustain their existence throughout the oscillation period by altering their size, shape, and strength, and a dome vortex is created twice each oscillation period (once from each jet). The dome vortex plays a key role in the kinetic energy transfer mechanism inside the oscillator by means of jet bifurcations. The primary oscillation mechanism in the transition regime is that each internal jet's connection with the exiting jet is cut completely by the dome vortex in every period. This is in contrast to the low-flow rate oscillation mechanism, in which the oscillations are created by continuous collisions of the jets. Furthermore, the internal jets are observed to energize the side vortex on the opposite side of the chamber-a phenomenon that was not observed in the low-flow rate regime.