Transition to turbulence and streamwise inhomogeneity of vortex tangle in thermal counterflow

TL;DR

This study combines experimental and numerical approaches to investigate the development and distribution of vortex tangles in superfluid helium-4 counterflow, revealing complex initial patterns but overall streamwise homogeneity in vortex line density.

Contribution

It provides new insights into the spatiotemporal evolution of vortex tangles in superfluid helium, combining experimental measurements with vortex filament simulations.

Findings

VLD is nearly homogeneous in steady state.

Initial VLD build-up shows complex spatial features.

Some tangle properties are uniform along the channel.

Abstract

We report preliminary results of the complementary experimental and numerical studies on spatiotemporal tangle development and streamwise vortex line density (VLD) distribution in counterflowing $^4$He. The experiment is set up in a long square channel with VLD and local temperature measured in three streamwise locations. In the steady state we observe nearly streamwise-homogeneous VLD. Experimental second sound data as well as numerical data (vortex filament method in a long planar channel starting with seeding vortices localized in multiple locations) show that the initial build up pattern of VLD displays complex features depending on the position in the channel, but the some tangle properties appear uniform along its length.