# $^4$He Counterflow Differs Strongly from Classical Flows: Anisotropy on Small Scales

## TL;DR

This paper reveals that superfluid helium-4 counterflow turbulence becomes more anisotropic and quasi-2D at smaller scales, contrasting classical turbulence behavior, supported by theoretical analysis and simulations.

## Contribution

It demonstrates that superfluid $^4$He turbulence in counterflow diverges from classical turbulence by increasing anisotropy at smaller scales, supported by new theory and simulations.

## Key findings

- Superfluid $^4$He turbulence becomes less isotropic at smaller scales.
- The flow transitions to a quasi-2D state at small scales.
- The phenomenon is explained through physical theory and numerical simulations.

## Abstract

Three-dimensional anisotropic turbulence in classical fluids tends towards isotropy and homogeneity with decreasing scales, allowing --eventually-- the abstract model of "isotropic homogeneous turbulence" to be relevant. We show here that the opposite is true for superfluid $^4$He turbulence in 3-dimensional counterflow channel geometry. This flow becomes less isotropic upon decreasing scales, becoming eventually quasi 2-dimensional. The physical reason for this unusual phenomenon is elucidated and supported by theory and simulations.