Effects of nozzle geometry on the evolution of three-dimensional twin synthetic jets

The effects of nozzle geometry on the evolution of three-dimensional in-phase twin synthetic jets issuing into a quiescent medium were investigated using improved delayed detached eddy simulation. Five orifice geometries were examined: circle, square, rectangle (two orientations, aspect ratio of 3), and ellipse (aspect ratio of 3), with a fixed spacing ratio of s/d=2, cross-sectional area, and actuation parameters. The Reynolds number, based on the spatially averaged jet exit velocity, was approximately 120 to ensure the generation of discrete vortex rings in the near field. The results show that nozzle geometry primarily influences the near-field behavior, while the combined jet demonstrates similarity in the far field. Rectangular and elliptical nozzles promote self-induced deformation and axis-switching of individual vortex rings near the exit before merging, thereby enhancing entrainment and shortening potential core lengths. However, within the merging region, the circular and square cases exhibit significantly stronger entrainment driven by axis-switching of the merged vortex rings. The merged rings undergo axis-switching before the combined point in all cases except for the rectangular nozzle with its major axis parallel to the symmetry line, for which axis-switching occurs after the combined point. Circular and square nozzles exhibit similar flow development owing to the rapid corner-induced deformation of the square rings near the exit, while rectangular and elliptical nozzles of similar orientation likewise display comparable behavior.