Backreaction of tracer particles on vortex tangle in helium II counterflow

TL;DR

This paper uses computer simulations to study how seeding particles influence the vortex tangle in superfluid helium-4 counterflow, revealing that high particle concentrations can alter vortex properties and affect visualization techniques.

Contribution

The study demonstrates how particle concentration impacts vortex tangle dynamics, highlighting potential issues in visualization experiments and distinguishing effects based on particle density.

Findings

High particle concentration increases vortex line density.

Large particles alter vortex tangle polarization.

Particle image velocimetry may significantly affect vortex properties.

Abstract

We report computer simulations of the interaction of seeding particles with quantized vortices and with the normal fluid flow in thermal counterflow of superfluid $^4$He. We show that if the particle concentration is too large, the vortex tangle is significantly affected, posing problems in the interpretation of visualization experiments. The main effects are an increase in vortex line density and a change in polarization of the vortex tangle, caused by the action of the Stokes drag of the viscous normal fluid on the trapped particles. We argue that in the case of large particle concentration, typically used for the particle image velocimetry technique, the tangle properties might become significantly changed. On the contrary, the particle tracking velocimetry technique that uses smaller particle concentration should not be appreciably affected.