Abstract
Mixing of gaseous jets in a cross-flow has significant applications in engineering, one example of which is the dilution zone of a gas turbine combustor. Despite years of study, the design of jet injection in combustors is largely based on practical experience. A series of experiments was undertaken to delineate the optimal mixer orifice geometry. A cross-flow to core-flow momentum-flux ratio of 40 and a mass flow ratio of 2.5 were selected as representative of an advanced design. An experimental test matrix was designed around three variables: the number of orifices, the orifice aspect ratio (long-to-short dimension), and the orifice angle. A regression analysis was performed on the data to arrive at an interpolating equation that predicted the mixing performance of orifice geometry combinations within the range of the test matrix parameters. Results indicate that mixture uniformity is a non-linear function of the number of orifices, the orifice aspect ratio, and the orifice angle. Optimum mixing occurs when the asymptotic mean jet trajectories are in the range of 0.35 less than r/R less than 0.5 (where r = 0 is at the mixer wall) at z/R = 1.0. At the optimum number of orifices, the difference between shallow-angled slots with large aspect ratios and round holes is minimal and either approach will lead to good mixing performance. At the optimum number of orifices, it appears possible to have two local optimums where one corresponds to an aspect ratio of 1.0 and the other to a high aspect ratio.
Highlights
M IXING of air jets into a cross ow is a fundamentalpart of gas turbine engine technology
Many studies of con ned jet mixing have been conducted on combustor components for advanced gas turbine engines
The optimization experiments resulted in the following conclusions: 1) Mixture uniformity is a nonlinear function of the number of ori ces, the ori ce long-to-short AR, and the ori ce angle
Summary
M IXING of air jets into a cross ow is a fundamentalpart of gas turbine engine technology. It was observed that the optimum mixing con guration varied in the number of ori ces at a xed momentum- ux ratio. Oechsle et al.7 considered the optimization requirements of the different ori ce designs reported by Hatch et al.5 Oechsle et al.7 used several different parameters for optimization including an area weighted standard deviation, and concluded that the relatively shallow-angledslanted slot ori ces would provide optimum jet penetration and mixing characteristics.
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