Abstract
Vortex dipoles are fundamental in fluid mechanics. They are found in geophysics, engineering and industry. The two necessary conditions to generate them are a plane flow and a generating force. In this work, an experimental design to generate vortex dipoles in stratified beds is presented. Vortex rings were generated under diferent volumetric flow conditions. Through visualization techniques, three stages were observed during the evolution of the rings: an exponential stage associated with the injection of the tracer, a parabolic stage and finally a dissipative stage. From the experimental results, the Reynolds and Péclet numbers were computed indicating laminar flows and difusive flows, respectively.
Highlights
A vortex dipole is an axial flow with two vortices of equal strength but opposite sign travelling through a fluid
Vortex dipoles are very stable structures and decay only when their kinetic energy is almost completely dissipated by friction
A simple and economical experimental design to generate vortex rings in a stratified bed was presented, following the Afasanayev design [10], but introducing an automatized injection system and an antivibrational aired container. The former allows an accurate experiment’s repeatability. The latter avoid the interaction between the external vibrations and the dipole dynamics
Summary
A vortex dipole is an axial flow with two vortices of equal strength but opposite sign travelling through a fluid. Due to the fluid’s viscosity, the vorticity spreads over a larger area and the dipole decreases in strength, it slows down and spirals towards the centre of the domain. The fluid flows along the streamlines, around the extreme of vorticity; the maximum velocity, in the positive x direction, occurs at the dipole axis [1]. One half of the dipole has positive vorticity, whereas the other half has negative vorticity, its total circulation is zero. Outside this circle there is no vorticity and the flow is potential.
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