Structure of a particle-laden round jet

TLDR

Solid particles interacting with turbulent flows are crucial for combustion and particulate processing applications. The study investigates particle behavior in a jet dominated by vortex ring structures. An axisymmetric air jet carrying 55‑µm glass particles was acoustically forced to generate vortex rings, and the flow was visualized with a pulsed copper‑vapor laser at Re≈20 000. Particles cluster in the saddle regions of vortex rings and are expelled from the jet axis by outward flow, with dispersion governed by large‑scale turbulence that persists up to a particle‑to‑air mass loading of 0.65.

Abstract

The interaction of solid particles with the temporal features of a turbulent flow has direct relevance to problems in particle and spray combustion and the processing of particulate solids. The object of the present study was to examine the behaviour of particles in a jet dominated by vortex ring structures. An axisymmetric air jet laden with 55 μm glass particles was forced axially with an acoustic speaker to organize the vortex ring structures rolling up in the free shear layer downstream of the nozzle exit. Visualization studies of forced and unforced flow with Reynolds number of the order of 20000 were completed using a pulsed copper vapour laser. Instantaneous photographs and videotapes of strobed forced flow show that particles become clustered in the saddle regions downstream of the vortex rings and are propelled away from the jet axis by the outwardly moving flow in these regions. Phase-averaged spatial distribution of particle number density computed from digitized photographs and phase-averaged particle velocity measurements yield further evidence that local particle dispersion and concentration are governed by convection due to large-scale turbulence structures. The large-scale structures and convection mechanisms were shown to persist for particle-to-air mass loading ratios up to 0.65.