Vortex dominated flow fields in jets from notched circular nozzles

Abstract

The vortex dominated flow field in jets from notched circular nozzles is investigated using numerical simulation. The nozzle denoted as S-shape notched nozzle (S-nozzle) considered in the present study has a lip which is shaped by a sine wave with two peaks and two troughs. A normal circular nozzle with the same circular cross-section is also considered both for comparison and for a better understanding of the vortex formed in the jet flow field. The vortex dynamics resulting from these two different nozzles were visualized by using a novel numerical dye visualization technique. The results indicated that the generation of streamwise vortex-pairs is due to the interaction between two opposite motions; the inward motion of the ambient fluid towards the jet axis and outwardly spreading motion of jet fluid, induced by two neighboring primary vortex-rings. These streamwise vortex-pairs are generated inside and also outside the vortex-rings and spread outward as the vortex-rings convect downstream. Comparison of the S-nozzles flow shows that for the notched S-nozzles, streamwise vortex-pairs are produced only at the peak and trough locations, in the course of the formation of azimuthal vortex-rings. This is unlike the circular nozzle where the number of streamwise vortex-pairs formed would depend on Reynolds number.