Non-isothermal mixing characteristics in the extreme near-field of a turbulent jet in hot crossflow

Abstract

The nonreacting and reacting jet in crossflow (JICF) is an important flow configuration for effective mixing and combustion in practical applications. Many studies in the literature exist that examine the overall mixing characteristics of an isothermal, unconfined, nonreacting JICF. This experimental study examines the mixing characteristics in the very near field (s/d ≤ 3) of a nonreacting jet in a hot crossflow of combustion products (1500 K), a configuration relevant to gas turbine combustion. A range of jet-to-crossflow momentum flux ratios (5.2 ≤ J ≤ 24.2) and jet-to-crossflow density ratios (3.2 ≤ ρj/ρcf ≤ 7.8) was studied for a round jet with fully developed turbulent pipe flow and 4% mean turbulence intensity at the jet exit. Temperature measurements were made using planar laser Rayleigh scattering. Jet trajectory, jet centerline concentration decay based on adiabatic mixing assumption, Favre-averaged scalar dissipation, and scalar mixing time scales were determined as a function of the above-mentioned jet parameters. 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 in the extreme near field of the jet. As the momentum flux ratio was increased, windward and leeward mixing around the elongated potential core decreased, as indicated by the relative temperatures in these regions. The magnitude of scalar dissipation in the windward region decreased as the jet momentum flux increased, while the leeward dissipation region increased in size and magnitude as the momentum flux ratio increased. When the density ratio was decreased toward unity, both the windward and leeward dissipation regions reduced in size and magnitude.