Renormalisation of particle distributions in an initially-biased turbulent jet by swirl and radial injection

Abstract

The distribution of particles in a jet with an initial bias is assessed using planar nephelometry, which is a planar imaging technique using Mie-scattering. Initial biases in particle distributions can have large and significant effects, particularly in solid fuel combustion systems, where inhomogeneities will affect the local and global performance of a flame. In this study, a two-phase jet flow with a controlled initial bias is generated at a Stokes number, based on the large-eddy time-scale, of Sk(D) = 0.39, and various strategies are explored to correct this bias. The investigation examines the usefulness of injecting air at various momentum ratios and through various configurations upstream from the nozzle exit plane. The study examines the differential roles of swirl (tangential) and radial injection of air at various locations from the flow exit. Radial injection of momentum is found to be superior to injection of swirl, consistent with swirl being a magnifier of eccentricities of a flow. Radial injection upstream from the nozzle can achieve a re-homogenised flow to develop prior to the exit, at least for the present Stokes numbers, but can also lead to downstream biases in particle distribution for some conditions. Injecting momentum directly at the nozzle exit does not allow a symmetrical distribution to be achieved, but does have an observed influence on the emerging flow-field.