Near Field Mixing Characteristics of a Variable Density Non-Reacting Jet in a Hot Vitiated Crossflow

The mixing characteristics in the “extreme” near field of a non-reacting jet in crossflow were experimentally investigated in an environment relevant to gas turbine combustors. A turbulent jet was injected into a hot vitiated crossflow of combustion products at 1500K. Different jet-to-crossflow momentum flux ratios and jet-to-crossflow density ratios were studied using three different jet exit velocity profiles; a fully developed turbulent pipe flow with 4% turbulence intensity (TI), a top-hat flow with 8% TI, and a turbulent pipe-like flow with 40% TI. Center-plane scalar mixing of the jet and crossflow were investigated using measured temperature fields from planar laser Rayleigh scattering. Jet trajectory, centerline concentration decay, scalar dissipation and mixing time scales were determined as a function of the above-mentioned jet parameters to characterize the jet-crossflow mixing characteristics. The observed center-plane mixing metrics indicated that better near field mixing was exhibited for lower values of the momentum flux ratio and larger values of density ratio. As the momentum flux ratio increased, windward and leeward mixing decreased. The magnitude of scalar dissipation in the windward region decreased as the momentum flux increased, while the leeward dissipation region increased in size and magnitude as momentum flux ratio increased. When the density ratio was decreased, both the windward and leeward dissipation regions reduced in size and magnitude. The top-hat and turbulent pipe jet exit velocity profiles displayed similar mixing characteristics while the 40% TI profile exhibited deeper jet penetration, slower centerline concentration decay rates, and lower scalar dissipation