NUMERICAL-SIMULATION OF NONCIRCULAR JETS

Results are presented of numerical simulations of spatially developing, three-dimensional jets issued from circular and non-circular nozzles of identical equivalent diameters. Elliptic, rectangular and triangular jets are considered with aspect-ratios of 1:1 and 2:1. Flow visualization results show that large scale coherent structures are formed in both cornered and non-cornered jets. The axis-switching phenomenon is captured in all non-unity aspect-ratio jets and also in the equilateral triangular jet. The square jet does not show axis-switching; however, the rotation of its axes by 45-degrees is shown to play a significant role in its entrainment characteristics. All the non-circular configurations are shown to provide more efficient mixers than does the circular jet; the isosceles triangular jet is the most efficient one. It is demonstrated that the near field entrainment and mixing is characterized by the mean secondary flow induced by the stream-wise vortices. The transport of a passive Shvab-Zeldovich scalar variable is used to determine the limiting rate of mean reactant conversion in a chemical reaction of the type Fuel + Air --> Products. The results show that the largest product formation occurs in the isosceles triangular jet and the lowest occurs in the circular jet. It is also shown that the 2:1 triangular jet has the shortest scalar core whereas the rectangular jet has the longest core.