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Open Access Publications from the University of California

Optimization of orifice geometry for crossflow mixing in a cylindrical duct

  • Author(s): Kroll, JT
  • Sowa, WA
  • Samuelsen, GS
  • Holdeman, JD
  • et al.

Published Web Location Commons Attribution 4.0 International Public License

Mixing of gaseous jets in a crossflow has significant applications in combustion science and engineering, one example of which is the mixing zone of a rich-burn/quick-mix/lean-burn gas turbine combustor. A major design question is the jet orifice shape and jet orifice number that optimizes the mixing performance. To delineate the optimal orifice features for a given axial distance and momentum-flux ratio, a statistical design of experiments test matrix was established around three variables: the number of orifices, the orifice aspect ratio, and the orifice angle (in circumferential plane). A jet-to-mainstream momentum-flux ratio of 40 and a mass-flow ratio of 2.5 were selected as representative of a practical design. To yield an interpolating equation that predicts the mixing performance of orifice geometry combinations within the range of the test matrix parameters, a regression analysis was conducted on the data. The results reveal that 1) mixture uniformity is a nonlinear function of the number of orifices, the orifice aspect ratio, and the orifice angle and that 2) optimum mixing occurs when the mean jet trajectories are in the range of 0.30<ζ/R<0.5 (where ζ = R-r) at x/R = 1. At the optimum number of orifices, the difference between shallow-angled slots with large aspect ratios and round holes is minimal and either geometry produces optimal mixing performance.

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