Measurements of the particle-fluid velocity correlation and the extra dissipation in a round jet

Abstract

Measurements of the particle/fluid velocity correlation and the dissipation of turbulent kinetic energy by particles were made in the near field of an axisymmetric jet laden with either 55 or 86 μm diameter glass beads. A digital particle-image-velocimetry system was adapted to measure simultaneously the velocity of fine tracer particles and larger dispersed particles. The particle/fluid velocity correlation was measured directly using the simultaneous measurements and indirectly using separate phase-locked measurements in an acoustically-forced jet. The direct measurements produced correlation values which were too low and the indirect measurements were too high, so the two techniques bracketed the correlation. Surprisingly, the correlation increased with increasing particle time-constant because the mean velocity of the heavier particles was closer to the convection velocity of the vortex rings in the jet. The dissipation of fluid turbulent kinetic energy by the particles was calculated using the phase-locked velocity measurements along with phase-locked particle concentration measurements. The results showed that the extra dissipation is large near the jet centerline, but quite small in the shear layer where the production is large.