MIXING OF MULTIPLE JETS WITH A CONFINED SUBSONIC CROSS-FLOW

This paper summarizes experimental and computational results on the mi xing of single, double, and opposed rows of jets with an isothermal or variable temperature mainstream in a confined subsonic crossflow. The studies from which these results came were performed to investigate f low and geometric variations typical of the complex three-dimensional flowfield in the dilution zone of combustion chambers in gas turbine e ngines. The principal observations from the experiments were that the momentum-flux ratio was the most significant flow variable, and that t emperature distributions were similar, independent of orifice diameter , when the orifice spacing and the square-root of the momentum-flux ra tio were inversely proportional. The experiments and empirical model f or the mixing of a single row of jets from round holes were extended t o include several variations typical of gas turbine combustors, namely variable temperature mainstream, flow area convergence, noncircular o rifices, and double and opposed rows of jets, both in-line and stagger ed. All except the last of these were appropriately modeled with super position or patches to the basic empirical model. Combinations of flow and geometry that gave optimum mixing were identified from the experi mental and computational results. Based on the results of calculations made with a three-dimensional numerical model, the empirical model wa s further extended to model the effects of curvature and convergence. The principal conclusions from this study were that the orifice spacin g and momentum-flux relationships were the same as observed previously in a straight duct, but the jet structure was significantly different for jets injected from the inner wall of a turn than for those inject ed from the outer wall. Also, curvature in the axial direction caused a drift of the jet trajectories toward the inner wall, but the mixing in a turning and converging channel did not seem to be inhibited by th e convergence, independent of whether the contraction was radial or ci rcumferential. The calculated jet penetration and mixing in an annulus were similar to those in a rectangular duct when the orifice spacing was specified at the radius dividing the annulus into equal areas.