title: Experimental observation of nonlinear traveling waves in turbulent pipe flow.
abstract: Transition to turbulence in pipe flow is one of the most fundamental and longest-standing problems in fluid dynamics. Stability theory suggests that the flow remains laminar for all flow rates, but in practice pipe flow becomes turbulent even at moderate speeds. This transition drastically affects the transport efficiency of mass, momentum, and heat. On the basis of the recent discovery of unstable traveling waves in computational studies of the Navier-Stokes equations and ideas from dynamical systems theory, a model for the transition process has been suggested. We report experimental observation of these traveling waves in pipe flow, confirming the proposed transition scenario and suggesting that the dynamics associated with these unstable states may indeed capture the nature of fluid turbulence.
authors.affiliation: Laboratory of Aerodynamics and Hydrodynamics, Delft University of Technology, Leeghwaterstraat 21, 2628 CA Delft, Netherlands. b.hof@wbmt.tudelft.nl
authors.forename: Björn
authors.initials: B
authors.lastname: Hof
authors.forename: Casimir W H
authors.initials: CW
authors.lastname: van Doorne
authors.forename: Jerry
authors.initials: J
authors.lastname: Westerweel
authors.forename: Frans T M
authors.initials: FT
authors.lastname: Nieuwstadt
authors.forename: Holger
authors.initials: H
authors.lastname: Faisst
authors.forename: Bruno
authors.initials: B
authors.lastname: Eckhardt
authors.forename: Hakan
authors.initials: H
authors.lastname: Wedin
authors.forename: Richard R
authors.initials: RR
authors.lastname: Kerswell
authors.forename: Fabian
authors.initials: F
authors.lastname: Waleffe