Comparative study on interfacial oscillations of rectangular and elliptical liquid jets

Abstract

The instability characteristics and flow structures of water jets injected from rectangular and elliptical nozzles with aspect ratios varying from 2 to 6 were experimentally studied and compared. Shadowgraph technique was employed for flow visualization, and structures on the liquid jet surface were captured using high speed photography. It was found that disturbances originating from the nozzle geometry initially perturbed the liquid column, and then, at high jet velocities, disturbances generated within the flow dominated the jet surface. It was also found that rectangular nozzles introduced more disturbances into the flow than the elliptical ones. The characteristic parameters of axis-switching phenomenon including wavelength, frequency, and amplitude were measured and compared. Axis-switching wavelength was found to increase linearly with Weber number. Also, the wavelengths of rectangular jets were longer than the elliptical jets. Further, the frequency of axis-switching was shown to be reduced with increase of both Weber number and aspect ratio. It was observed that the axis-switching amplitude increased monotonically, reached a peak, and then decreased gradually. It was also found that the axis-switching amplitude varied with Weber number. At lower values of Weber number, the rectangular nozzles had higher amplitude than the elliptical nozzles. However, at higher values of Weber number, this relation was reversed, and the elliptical nozzles had the higher axis-switching amplitudes. This reversal Weber number decreased with the orifice aspect ratio. The reversal Weber number for aspect ratio of 4 was about 289, and it had decreased to 144 for the aspect ratio of 6.

Entrance length effects on the flow features of rectangular liquid jets

“…Further increase of Weber number was associated with the emergence of disturbances over the liquid surface. According to Jaberi and Tadjfar, 1 for rectangular liquid jets, part of these instabilities were induced from the vortical flow formed in the corners. However, increasing the jet velocity led to the intensification of Kelvin-Helmholtz instabilities that were produced due to the velocity gradient at the interface of liquid flow and surrounding stagnant air.…”

“…As was mentioned in the introduction, these interfacial oscillations occur because of the competition between surface tension and lateral inertial forces. Though the effects of jet shape, 1,16 liquid properties 17 and aspect ratio 13,18 were previously investigated, no information was reported so far on the influence of entrance length on the axis-switching characteristics. In this section, the dependency of the main characteristics of axis-switching phenomenon on the entrance length would be discussed.…”

“…Agricultural irrigation systems, medical inhalers, inkjet printers, fuel spray systems, and inkjet printing are the most relevant examples. 1 Moreover, from an academic view, studying the underlying physics of these flows are very interesting. This is due to the complicated interaction of several forces that simultaneously act on the liquid jet.…”

Chain oscillations in liquid jets

“…They found that the amplitude of the octapolar (azimuthal dependence cos 4θ ) component of the jet's shape relative to the quadrupolar (cos 2θ ) component agreed closely with Bohr's nonlinear theory. Jaberi and Tadjfar [18,19] used laboratory experiments to compare axis switching with elliptical and square nozzles. Ma and Zhu [20] performed experiments on axis switching in elliptical jets and proposed a way to correct the switching frequency for the effect of gravity.…”