Multi-Jet Annulus/Core-Flow Mixing—Experiments and Calculations

Abstract

LDV measurements are reported of the flow-field associated with a single row of radially injected jets penetrating a core-tube flow. Emphasis is placed on the influence of small feed-annulus height on jet entry conditions and resulting trajectories and mixing patterns. Conditions of unstable jet behaviour, with strong vortex patterns in the jet holes, were observed for small annulus heights and high annulus velocities. Most measurements were however taken under stable conditions to allow the data to be used in a CFD validation exercise. Significant differences in the strength of backflow generated at jet impingement and in the turbulence field in the immediate hole vicinity were observed for different annulus height/core diameter ratios. These were accompanied by jet trajectory and annulus flow structure changes. Measurements of all 3 mean velocity components and associated normal stresses enabled the data to be utilised to assess a 3D CFD calculation incorporating a k-ε turbulence closure. The strength of forward and back flow generated at impingement was accurately predicted when the QUICK discretisation scheme was used. However, the size of upstream vortex was overpredicted. As expected using an eddy viscosity model the turbulence field at jet impingement and in the hole vicinity was not correctly reproduced. The turbulence generation in the flow approaching the hole was greatly overestimated by the turbulence model used.