The influence of Stokes number on particle clustering within a two-phase turbulent jet

Abstract

The effect of the particle Stokes number on the clustering of solid particles in the near field of a two-phase, turbulent, jet issuing from a long, round, pipe into a low velocity co-flow is investigated through the use of planar nephelometry and statistical box counting. The exit Stokes number was varied two orders of magnitude between 0:3 ≤ Sk0 ≤ 22:4, which resulted in a Reynolds number of 10;000 ≤ ReD ≤ 40; 000. The particle mass loading was fixed at ⏀ = 0:4, resulting in a flow that is in the two-way coupling regime. The results show that the phenomenon of particle clustering at the jet exit is significantly influenced by the exit Stokes number for 0:3 ≤ Sk0 ≤ 5:6. The degree of particle clustering was highest at the lowest investigated Stokes number, Sk0 = 0:3, and lowest for Sk0 > 5:6. Images of two-dimensional slices through three-dimensional clusters appeared as filament-like structures oriented at oblique angles across the jet, whose thickness increased with increasing Sk0. It is postulated that these clusters may be associated with persistent, large-scale streamwise structures that develop within the pipe and that turbophoresis augments particle clustering by causing the mean distribution of particles to be preferentially concentrated along the pipe boundary.