# Mean flow anisotropy without waves in rotating turbulence

## TL;DR

This paper reveals a new wave-free mechanism driven by the Coriolis force and advection that promotes flow anisotropy in rotating turbulence, challenging the traditional wave-based explanation.

## Contribution

It identifies a novel, non-wave mechanism involving the Coriolis force and advection that explains flow anisotropy in rapidly rotating turbulence.

## Key findings

- Anisotropy can arise without inertial waves.
- A new mechanism involving Coriolis force and advection is proposed.
- Experimental evidence supports the wave-free anisotropy mechanism.

## Abstract

We tackle the question of how anisotropy in flows subject to background rotation favours structures elongated along the rotation axis, especially in turbulent flows. A new, wave-free mechanism is identified that challenges the current understanding of the process. Inertial waves propagating near the rotation axis are generally accepted as the most efficient mechanism to transport energy anisotropically. They have been shown to transfer energy to large anisotropic, columnar structures. Nevertheless, they cannot account for the formation of simpler steady anisotropic phenomena such as Taylor columns. Here, we experimentally show that more than one mechanism involving the Coriolis force may promote anisotropy. In particular, in the limit of fast rotation, that is at low Rossby number, anisotropy favouring the direction of rotation of the average of a turbulent flow arises neither because of inertial waves nor following the same mechanism as in steady Taylor columns, but from an interplay between the Coriolis force and average advection.