Lagrangian velocity auto-correlations in statistically-steady rotating turbulence

TL;DR

This study investigates how rotation affects the Lagrangian velocity auto-correlations in turbulent flows, revealing anisotropy and changes in decorrelation behavior with increasing rotation rates using Particle Tracking Velocimetry.

Contribution

It provides new experimental insights into the anisotropic effects of rotation on Lagrangian velocity correlations in steady rotating turbulence.

Findings

Auto-correlation coefficients increase with rotation rate.

Vertical velocity correlations decrease at slow rotation rates.

Decorrelation follows an approximately exponential decay.

Abstract

Lagrangian statistics of passive tracers in rotating turbulence is investigated by Particle Tracking Velocimetry. A confined and steadily-forced turbulent flow is subjected to five different rotation rates. The PDFs of the velocity components clearly reveal the anisotropy induced by background rotation. Although the statistical properties of the horizontal turbulent flow field are approximately isotropic, in agreement with previously reported results by van Bokhoven and coworkers [Phys. Fluids 21, 096601 (2009)], the velocity component parallel to the (vertical) rotation axis gets strongly reduced (compared to the horizontal ones) while the rotation is increased. The auto-correlation coefficients of all three components are progressively enhanced for increasing rotation rates, although the vertical one shows a tendency to decrease for slow rotation rates. The decorrelation is approximately exponential. Lagrangian data compare favourably with previously reported Eulerian data for horizontal velocity components, but show different behaviour for the vertical velocity components at higher rotation rates.