Clarify the transition mechanism to elastic turbulence in pipe flow

Clarify the transition mechanism by which viscoelastic pipe flow reaches fully developed elastic turbulence, determining whether the route is mediated by a secondary instability distinct from the channel-flow instability or by a bypass-transition-like mechanism.

Background

The paper demonstrates sustained, fully chaotic elastic turbulence in a circular pipe, despite geometric constraints that prevent pipe flow from reproducing the transverse modulation associated with the channel-flow transition route. In particular, the pipe centreline cannot support a disturbance with nonzero streamwise velocity away from full axial symmetry in the same manner as a channel centre-plane.

The authors therefore infer that pipe flow must access the same elastic-turbulent attractor through a different mechanism. They identify a possible secondary instability distinct from the channel instability and a bypass-transition-like route, but do not determine which mechanism operates. The nature of this transition is explicitly left unresolved.

References

The attainment of ET in pipes thus implies the existence of an alternative route to chaos, possibly mediated by a secondary instability distinct from the one identified in channels, or by a mechanism akin to a bypass transition cite{itoh-1977, kerswell-2005, avila-barkley-hof-2022}. Clarifying the nature of this transition remains an open problem.

— Elastic turbulence in straight confined geometries  (2609.04617 - Rota et al., 4 Sep 2026) in Conclusion, paragraph beginning “This has direct implications for viscoelastic pipe flow”