Intermittency of velocity circulation in quantum turbulence

TL;DR

This study investigates how velocity circulation behaves across different scales in quantum turbulence, revealing intermittent behavior at small scales and classical-like statistics at larger scales, highlighting universal turbulence features.

Contribution

It provides the first comprehensive analysis of circulation scale dependence in quantum turbulence, comparing quantum and classical flow statistics using high-resolution simulations.

Findings

Circulation in quantum turbulence shows extreme intermittency at scales below inter-vortex distance.

At larger scales, circulation statistics align with classical turbulence predictions.

Results support the universality of inertial range dynamics and intermittency across quantum and classical turbulence.

Abstract

The velocity circulation, a measure of the rotation of a fluid within a closed path, is a fundamental observable in classical and quantum flows. It is indeed a Lagrangian invariant in inviscid classical fluids. In quantum flows, circulation is quantized, taking discrete values that are directly related to the number and the orientation of thin vortex filaments enclosed by the path. By varying the size of such closed loop, the circulation provides a measure of the dependence of the flow structure on the considered scale. Here we consider the scale dependence of circulation statistics in quantum turbulence, using high resolution direct numerical simulations of a generalized Gross-Pitaevskii model. Results are compared to the circulation statistics obtained from simulations of the incompressible Navier-Stokes equations. When the integration path is smaller than the mean inter-vortex distance, the statistics of circulation in quantum turbulence displays extreme intermittent behavior due to the quantization of circulation, in stark contrast with the viscous scales of classical flows. In contrast, at larger scales, circulation moments display striking similarities with the statistics probed in the inertial range of classical turbulence. This includes the emergence of the power law scalings predicted from Kolmogorov's 1941 theory, as well as intermittency deviations that closely follow the recently proposed bifractal model for circulation moments in classical flows. To date, this is the most convincing evidence of intermittency in the large scales of quantum turbulence. Moreover, our results strongly reinforce the resemblance between classical and quantum turbulence, highlighting the universality of inertial range dynamics, including intermittency, across these two a priori very different systems.