Optimization of Jet Mixing into a Rich, Reacting Crossflow

Radial jet mixing of pure air into a fuel-rich, reacting crossflow confined to a cylindrical geometry is addressed with a focus on establishing an optimal number of jet orifices. Note that the optimum would not be expected to be universal. That is, the optimum mixer that one would identify will depend on both the momentum-flux ratio and an axial distance appropriate to the application. The number of round holes that most efficiently mixes the jets with the mainstream flow, and thereby minimizes the residence time of near-stoichiometric and unreacted packets, was determined. Such a condition might reduce pollutant formation in axially staged, gas turbine combustor systems. Five different configurations consisting of 8, 10, 12, 14, and 18 round holes are reported. An optimum number of jet orifices is found for a jet to mainstream momentum-flux ratio J of 57 and a mass-flow ratio (MR) of 2.5. For this condition, the 14-orifice case produces the lowest spatial unmixedness and the most uniformly distributed species concentration and temperature profiles at a plane located an axial distance equal to one duct diameter from the jet orifice inlet. Note that this is the same configuration that would be identified from non-reacting experiments.