Destabilizing turbulence in pipe flow

TL;DR

This paper shows that in pipe flow, specific velocity profile distortions can completely eliminate turbulence, drastically reducing friction losses by up to 95%, through a mechanism involving eddy-shear interactions.

Contribution

It introduces a novel method to fully suppress turbulence in pipe flow by profile distortions, leading to potential energy savings in transport systems.

Findings

Turbulence can be collapsed with velocity profile distortions.

Friction losses are reduced by up to 95%.

Relaminarization occurs despite initial turbulence amplification.

Abstract

Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities, so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 95%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. The usual measures of turbulence levels, such as the Reynolds number (Re) or shear stresses, do not account for the subsequent relaminarization. Instead an amplification mechanism measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.