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An experimental study using Particle Image Velocimetry (PIV) on free jets issuing from sharp edge nozzles having different cross-section geometries is reported: elliptical, square, rectangular and triangular. The mixing efficiency of each nozzle is quantified at large and small scales. In respect to the large scales contribution, the definition of mixedness is used, while for small-scales, the entropy generation concept is employed. These quantities are computed to evaluate the mixing efficiency in the near field and interaction zone (0<X/D<18) of each nozzle. The effect of Reynolds number on the differences among the nozzle shapes is also discussed by performing measurements just after the laminar-turbulent transition (Re=8000) and in the fully turbulent regime(Re=35000). The results are also compared to the circular nozzle data to define changes in mixing efficiency among axisymmetric and asymmetric nozzles. The results show significant differences on major and minor axis of nozzles confirming the presence of axis switching features for elongated nozzles (elliptical and rectangular). Specifically, axis switching improves small scale mixing efficiency locally in the nozzle near field, while being less efficient in the far field in comparison to circular and square nozzles.
Author(s):
Giovanni Romano
Dept. Mechanical & Aerospace Engineering, University La Sapienza, Roma
Italy
Adel Hashiehbaf
Dept. Mechanical & Aerospace Engineering, University La Sapienza, Roma
Italy