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Axis switching of a jet ejected from a rectangular nozzle affects flow mixingcharacteristics. To elucidate such a mixing mechanism, the axis switching andvortex structure deformation should be investigated in detail. This studyperformed a numerical analysis of the axis switching of a pulsating jet ejectedfrom a rectangular nozzle at a low Reynolds number. At all aspect ratios, arectangular vortex ring similar to the shape of the nozzle cross-section isperiodically shed downstream, and the side of the vortex ring deforms into ahairpin shape downstream. A vortex pair is generated inside the vortex ringdownstream of the nozzle corner. When the aspect ratio is AR=1.0, the vortexpair consists of symmetrical vortices, while as AR increases, the asymmetry ofthe vortex pair enlarges. At AR=1.0, regeneration of a vortex ring occursdownstream. For AR=2.0, alternately on the long and short sides of the nozzle,an upstream vortex ring overtakes a downstream vortex ring. Regardless of AR,downstream near the nozzle, as the vortex pair existing inside the vortex ringdistorts the vortex ring, the positions of the side and corner of the vortexring exchange, resulting in a 45-degree axis switching. For AR>1.0, furtherdownstream, the hairpin part of the vortex ring on the long side develops awayfrom the jet center compared to the short side, causing a 90-degree axisswitching. As a result, high turbulence occurs over a wide area, strengtheningthe mixing action. As AR increases, intensive interference between the vortexrings on the upstream and downstream sides diffuses the vortices downstream.Then, as turbulence by the diffused vortices widely occurs, the mixing effectis further strengthened.

Numerical simulation for axis switching of pulsating jet issued from rectangular nozzle at low Reynolds number