| Summary: | A detailed study has been performed to investigate passive scalar mixing of turbulent co-flowing jets in their initial exhaust development region, as a complement to separate experimental studies, to provide better defined initial conditions for subsequent simpler model predictions of the effect of aircraft engine plume/vortex interactions on air quality. Accordingly a well-established Large Eddy Simulation (LES) technique has first been validated against experimental data for a low-speed turbulent round jet and then used to perform a parametric series of simulations, numerical experiments, for a coaxial jet representative of a modern, large by-pass ratio jet engine exhaust under a variety of conditions with passive scalar introduced into either the core or bypass flow. Effects of free-stream velocity, swirl, and boundary proximity have all been considered and conclusions drawn. The comparisons between LES data and experiment measurements were in good agreement for low-velocity round jet. For a higher-velocity coaxial jet, initial instabilities on the shear boundary between the core and by-pass flows were seen to quickly develop into large scale coherent (vortex) motions which grew in scale and lost energy to a broader range of motions at downstream. The numerical databases generated for this series of coaxial jet configurations provide a valuable source of information for more accurately initialising lower order modelling of subsequent jet efflux development and vortex interaction.
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