Energy and Vorticity Spectra in Turbulent Superfluid $^4$He from $T=0$ to $T_\lambda$

TL;DR

This paper analyzes the energy and vorticity spectra of turbulent superfluid helium-4 across all temperatures up to the lambda transition, highlighting the effects of quantized vorticity and mutual friction on turbulence scales and energy transfer.

Contribution

It provides a comprehensive description of the spectra in superfluid helium-4, incorporating quantized vorticity scales and the impact of mutual friction, extending understanding from zero to near-critical temperatures.

Findings

Identification of multiple turbulence scales including vortex core radius and mean vortex spacing.

Demonstration that mutual friction suppresses the Kelvin wave energy bottleneck.

Estimation of the effective viscosity $ u'$ consistent with experimental data.

Abstract

We discuss the energy and vorticity spectra of turbulent superfluid $^4$He in all the temperature range from $T=0$ up to the phase transition "$\lambda$ point", $T_\lambda\simeq 2.17\,$K. Contrary to classical developed turbulence in which there are only two typical scales, i.e. the energy injection $L$ and the dissipation scales $\eta$, here the quantization of vorticity introduces two additional scales, i.e the vortex core radius $a_0$ and the mean vortex spacing $\ell$. We present these spectra for the super- and normal-fluid components in the entire range of scales from $L$ to $a_0$ including the cross-over scale $\ell$ where the hydrodynamic eddy-cascade is replaced by the cascade of Kelvin waves on individual vortices. At this scale a bottleneck accumulation of the energy was found earlier at $T=0$. We show that even very small mutual friction dramatically suppresses the bottleneck effect due to the dissipation of the Kelvin waves. Using our results for the spectra we estimate the Vinen "effective viscosity" $\nu'$ in the entire temperature range and show agreement with numerous experimental observation for $\nu'(T)$.