MIXING OF MULTIPLE JETS WITH A CONFINED SUBSONIC CROSS-FLOW .1. CYLINDRICAL DUCT

This paper summarizes NASA-supported experimental and computational re sults on the mixing of a role of jets with a confined subsonic crossfl ow in a cylindrical duct. The studies from which these results were ex cerpted investigated flow and geometric variations typical of the comp lex three-dimension flowfield in the combustion chambers in gas turbin e engines. The principal observations were that the momentum-flux rati o and the number of orifices were significant variables. Jet penetrati on was critical, and jet penetration decreased as either the number of orifices increased or the momentum-flux ratio decreased. It also appe ared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the number of orifi ces was proportional to the square root of the momentum-flux ratio. In the cylindrical geometry, planar variances are very sensitive to even ts in the near-wall region, so planar-averages must be considered in c ontext with the distributions. The mass-flow ratios and orifices inves tigated were often very large (mass-flow ratio > 1 and ratio of orific e area-to-mainstream cross-sectional area up to 0.5), and the axial pl anes of interest were sometimes near the orifice trailing edge. Three- dimensional flow as a key part of efficient mixing and was observed fo r all configurations. The results shown also seem to indicate that non reacting dimensionless scalar profiles can emulate the reacting flow e quivalence ratio distribution reasonably well. The results cited sugge st that further study may not necessarily lead to a universal ''rule o f thumb'' for mixer design for low esr emissions, because optimization will likely require an assessment for a specific application.