Control of long-range correlations in turbulence

TL;DR

This paper introduces an advanced active grid that allows precise control over the long-range correlations in turbulence, enabling systematic studies of turbulence structure and flow characteristics.

Contribution

The authors develop a new active grid with increased degrees of freedom to manipulate the long-range correlations in turbulent flows, a capability not available in previous experimental setups.

Findings

Controlled the correlation length in turbulence by adjusting grid motions.

Shaped the detailed form of the correlation function through grid movement.

Enabled systematic exploration of turbulence properties and flow regimes.

Abstract

The character of turbulence depends on where it develops. Turbulence near boundaries, for instance, is different than in a free stream. To elucidate the differences between flows, it is instructive to vary the structure of turbulence systematically, but there are few ways of stirring turbulence that make this possible. In other words, an experiment typically examines either a boundary layer or a free stream, say, and the structure of the turbulence is fixed by the geometry of the experiment. We introduce a new active grid with many more degrees of freedom than previous active grids. The additional degrees of freedom make it possible to control various properties of the turbulence. We show how long-range correlations in the turbulent velocity fluctuations can be shaped by changing the way the active grid moves. Specifically, we show how not only the correlation length but also the detailed shape of the correlation function depends on the correlations imposed in the motions of the grid. Until now, large-scale structure had not been adjustable in experiments. This new capability makes possible new systematic investigations into turbulence dissipation and dispersion, for example, and perhaps in flows that mimic features of boundary layers, free streams, and flows of intermediate character.