Collapse of turbulence in optimised curved pipe flow

TL;DR

This study demonstrates that geometric modifications in curved pipes, such as increased curvature and oval cross-sections, can passively relaminarize turbulent flow, significantly reducing pressure loss.

Contribution

It introduces a passive, geometry-based method to suppress turbulence in curved pipes, achieving over 50% pressure loss reduction in experiments and simulations.

Findings

Relaminarization achieved at high Reynolds numbers in curved pipes.

Pressure loss reduced by up to 53% compared to baseline configurations.

Geometric modifications disrupt turbulence regeneration cycles.

Abstract

The increased friction caused by turbulence is a significant contributor to energy consumption in the fluid-transport and piping industries. Here we describe a passive approach to reduce friction: we show that a local increase in streamwise flow curvature, combined with changing the circular cross-section to an oval, relaminarizes turbulent flow in curved pipes. We exemplify this effect in a $180^\circ$ bend at $Re_D = 10\,000$ and $20\,000$, well above the linear-stability limit. Curvature inhibits streamwise Reynolds stresses, and cross-sectional modifications weaken the secondary flow, together disrupting the near-wall regeneration cycle and collapsing turbulence. Simulations and experiments confirm that these geometric modifications suppress turbulence and reduce pressure loss by 53% and 36% compared with the baseline $180^\circ$ bend and an equal-length fully developed straight pipe, respectively. The results establish a passive, mechanism-based route to relaminarization in curved pipes with implications for energy-efficient control in other wall-bounded flows with curvature.