Impact of adjacent spray–plume interaction on far-field droplet characteristics in rotary slinger atomizers

Abstract

Slingers are a type of rotary atomizer in which liquid is injected through multiple orifices located around the periphery of a rotating disc. Despite previous studies on slingers, the interaction between spray–plumes from adjacent orifices remains poorly understood. This study aims to bridge that gap by investigating how these interactions influence spray characteristics through droplet collisions. Understanding the conditions that promote such interactions is crucial for optimizing atomization efficiency and performance. Our focus is to elucidate the underlying physics governing plume interaction. The experiments were performed in a slinger test facility utilizing three slinger discs with different numbers of orifices, $\tilde{n}$ (= 18, 4, 2) such that the number of adjacent orifices is higher for greater $\tilde{n}$. The visualization of primary liquid breakup and droplet size measurement results reveal that the liquid atomization is dictated by the liquid flow rate per orifice (${\dot{q}}_l$) rather than inlet flow rate (${\dot{Q}}_l$). For the same ${\dot{q}}_l$ and rotational speed in all three slinger discs, the liquid breakup mode is similar, yet the characteristic droplet size is higher for the disc with a greater $\tilde{n}$ (from 2- to 18-orifice disc). This is attributed to spray-plume interaction that promotes droplet collision and coalescence. Various statistical parameters were calculated, including radial distribution function ($\mathrm{RDF}$), droplet relative velocity ($V_{rel}$) and collision Weber number (${\mathrm{We}}_{col}$), which provide reasonable evidence of droplet collision in the spray. The current study offers valuable insight into the design and development of the rotary slinger atomizers.