On the vortex structures and behaviour of notched elliptic jets

[Display omitted] •Interactions between elliptic vortex and braid filaments accentuated by notches.•Major-plane notched nozzle produces congregated vortex-loops at jet centre.•Vortex roll-ups retained minor-plane notched nozzle exit shape the furthest.•Major- and minor-plane notched nozzles suppress and delay axis-switching respectively.•Major-plane notched nozzle produces better jet-mixing characteristics. An experimental study on jets issuing from symmetrically notched elliptic nozzles is reported here, where changes in the flow behaviour due to the notch orientation (i.e. along the major- or minor-plane, known as nozzles A and B respectively) are investigated as part of the overall understanding. Results show that for both notch orientations, the vortex filaments follow the nozzle contours closely immediately after they are formed. For nozzle A, rapid entanglement and stretching of braid filaments by vortex filaments produce vortex-loops along the jet centre region which promote jet entrainment. For nozzle B however, vortex filaments retain outlines resembling the nozzle exit contour the furthest before streamwise vortices with opposite rotational senses are produced. Rib structures are produced by nozzle A but not in nozzle B. Compared to a non-notched nozzle, formations of rib structures/streamwise vortices are accelerated and delayed for nozzles A and B respectively. Additionally, nozzle A is also observed to suppress axis-switching behaviour while nozzle B merely delays it. Furthermore, nozzle A produces larger changes to the momentum thicknesses along both major- and minor-planes. Lastly, compared to the reference nozzle, nozzles A and B produce faster and slower decays of the centreline velocity respectively.