Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part II—Opposed Rows of Orifices in Rectangular Ducts

TLDR

The study investigates mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts through experimental and computational analysis. Experimental and computational methods examined flow and geometric variations typical of three‑dimensional gas‑turbine combustion chamber flowfields. The key findings are that momentum‑flux ratio and orifice spacing most strongly influence jet penetration, with penetration decreasing as either parameter drops, while 3‑D flow is essential for efficient mixing; penetration remains similar when spacing scales inversely with the square‑root of the momentum‑flux ratio.

Abstract

This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio > 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5, respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.