Intrinsic and extrinsic vortex nucleation mechanisms in the flow

TL;DR

This paper introduces general vortex nucleation mechanisms in fluid flow, analyzing intrinsic and extrinsic pathways, and calculates critical velocities that align with experimental observations.

Contribution

It proposes universal vortex nucleation mechanisms based on hydrodynamic instability and provides a theoretical framework matching experimental data.

Findings

Extrinsic mechanism involves surface vorticity sheet formation reaching a critical size.

Intrinsic mechanism involves fluctuative generation of small vortex rings leading to vortex formation.

Calculated critical velocities agree with experimental measurements.

Abstract

We propose very general vortex nucleation mechanisms analogous to a hydrodynamic instability and calculate associated critical velocity in agreement with experiments. The creation of vortices via extrinsic mechanism is driven by a formation of the surface vorticity sheet created by the flow, which reaches a critical size. Such a sheet screens an attraction of a half-vortex ring to the wall, the barrier for the vortex nucleation disappears and the vortex nucleation is started. In the intrinsic mechanism the creation of a big vortex ring, which transforms into the vortex, is driven by a fluctuative generation of small vortex rings