An experimental study was conducted to investigate nozzle geometry effects on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free jets issuing from modified contoured nozzles (contoured nozzle with a sharp linear contraction). The cross-sections examined were round, square, equilateral triangle as well as ellipse and rectangle with aspect ratio of 2. For each nozzle shape, detailed velocity measurements were made using particle image velocimetry at a Reynolds number of 10000. It was observed that noncircular jets have shorter potential cores than their round counterparts and their lengths are comparable with those of orifice jets. In addition, the spread and decay rates and the levels of turbulence intensities are the highest in the jets issuing from the elliptic and rectangular nozzles, implying enhanced mixing in these jets. The results from the swirling strength analysis revealed that the rotational motions induced by vortices within the minor planes of the elliptic and rectangular jets are more intense than those observed in the other jets. Furthermore the obtained data indicate distinctly different flow characteristics in the major and minor planes of elliptic, rectangular and triangular jets due to their asymmetric shapes. The size of turbulence structures in all the jets studied increases with streamwise distance and the elliptic and rectangular jets contain the largest structures.

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