Effect of magnetic boundary conditions on the dynamo threshold of von Karman swirling flows

TL;DR

This study investigates how various magnetic boundary conditions influence the onset of dynamo action in von Karman swirling flows, revealing that high-magnetic-permeability boundaries lower the dynamo threshold.

Contribution

It provides an analytical assessment of the impact of different boundary conditions on the dynamo threshold in cylindrical von Karman flows, highlighting the benefits of high-magnetic-permeability materials.

Findings

High-magnetic-permeability boundaries reduce the dynamo threshold.

Implementing such boundaries throughout the flow yields the lowest threshold.

Boundary conditions significantly influence dynamo onset in swirling flows.

Abstract

We study the effect of different boundary conditions on the kinematic dynamo threshold of von Karman type swirling flows in a cylindrical geometry. Using an analytical test flow, we model different boundary conditions: insulating walls all over the flow, effect of sodium at rest on the cylinder side boundary, effect of sodium behind the impellers, effect of impellers or side wall made of a high-magnetic-permeability material. We find that using high-magnetic-permeability boundary conditions decreases the dynamo threshold, the minimum being achieved when they are implemented all over the flow.