The formation and post-formation processes of vortex rings discharged from laminar starting jets

Haojun Zheng, Lei Gao (Corresponding Author), Ching Man Yu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

Abstract

Motivated by biological systems, vortex rings can enhance the propulsive efficiency in industrial systems. To study the vortex properties during the formation and post-formation stages, impulsively starting jets are investigated by simulations. The effects of the stroke ratio and nozzle geometry are studied at a fixed jet Reynolds number of 2500. The stroke ratio at the formation number is found to be not enough to produce a vortex ring with maximum circulation. The stroke ratio is suggested to be about twice as large as the formation number. An alternative criterion based on the circulation ratio is proposed to describe the onset of pinch-off. This criterion states that the pinch-off would start when the vortex ring attains about 80% of the total jet circulation. During the formation stage, the scaling laws for vortex trajectories and circulation are proposed for continuous formation. By combining the suggested scaling relations and Saffman's velocity formula, the evolution of non-dimensional energy can be predicted. During the post-formation stage, the scaling laws for vortex properties (e.g., the vortex ring diameter, translational velocity, and circulation) are found to be independent of both the nozzle configuration and the vortex Reynolds number. On the grounds of the invariance of impulse in vortex decay, the scaling laws of vortex motion are derived for the non-dimensional energy, circulation, and diffusivity scale of the vortex core. In consequence, the normalized energy and circulation found in experiments can be successfully derived from the similarity model for both nozzle configurations.
Original languageEnglish
Article number103601
JournalPhysics of Fluids
Volume36
Issue number10
DOIs
Publication statusPublished - Oct 2024

Keywords

  • Fluid jets
  • Laminar flows
  • Vortex dynamics
  • Viscous liquid

Fingerprint

Dive into the research topics of 'The formation and post-formation processes of vortex rings discharged from laminar starting jets'. Together they form a unique fingerprint.

Cite this