Coiling, entrainment, and hydrodynamic coupling of decelerated fluid jets

Area of Science:

• Fluid dynamics
• Geophysics
• Oceanography

Background:

• Jets in nature, from algal suspensions to magma, display symmetry-breaking instabilities.
• Standard momentum jets and plumes have well-defined behaviors.
• Saline jets in gradients present unique, uncharacterized dynamics.

Purpose of the Study:

• To investigate the distinct dynamics of a saline jet descending through a salinity gradient.
• To model the corkscrew coiling and fluid entrainment phenomena.
• To identify the underlying physical principles governing this jet behavior.

Main Methods:

• Developed a model system of a saline jet in a salinity gradient.
• Applied similarity solutions to fluid equations.
• Analyzed the physics of Kelvin-Helmholtz instabilities.

Main Results:

• Observed the jet coiling like a corkscrew within a conduit of entrained fluid.
• Demonstrated that upward recirculation braids the jet.
• Showed transverse mixing is largely confined to the narrow conduit.
• Identified jet structure and scaling relations from similarity solutions and instability physics.

Conclusions:

• The saline jet exhibits novel dynamics distinct from standard jets and plumes.
• Fluid entrainment and Kelvin-Helmholtz instabilities are key to the observed coiling and braiding.
• The study provides a framework for understanding complex jet behaviors in stratified environments.