Author(s):

Samanta, Devranjan; de Lózar, Alberto; Hof, Björn

Article Title: 
Experimental investigation of laminar turbulent intermittency in pipe flow

Affiliation 

Abstract: 
In shear flows, turbulence first occurs in the form of localized structures (puffs/spots) surrounded by laminar fluid. We here investigate such spatially intermittent flows in a pipe experiment showing that turbulent puffs have a welldefined interaction distance, which sets their minimum spacing as well as the maximum observable turbulent fraction. Two methodologies are employed. Starting from a laminar flow, puffs are first created by locally injecting a jet of fluid through the pipe wall. When the perturbation is applied periodically at low frequencies, as expected, a regular sequence of puffs is observed where the puff spacing is given by the ratio of the mean flow speed to the perturbation frequency. At large frequencies however puffs are found to interact and annihilate each other. Varying the perturbation frequency, an interaction distance is determined which sets the highest possible turbulence fraction. This enables us to establish an upper bound for the friction factor in the transitional regime, which provides a welldefined link between the Blasius and the HagenPoiseuille friction laws. In the second set of experiments, the Reynolds number is reduced suddenly from fully turbulent to the intermittent regime. The resulting flow reorganizes itself to a sequence of constant size puffs which, unlike in Couette and Taylor–Couette flow are randomly spaced. The minimum distance between the turbulent patches is identical to the puff interaction length. The puff interaction length is found to be in agreement with the wavelength of regular stripe and spiral patterns in plane Couette and Taylor–Couette flow.

Keywords: 
Upper Bound; Couette flows; Laminar fluids; Transition to turbulence; Mean flow; Blasius; Couette; Experimental investigations; Friction factors; Friction laws; HagenPoiseuille; Inplane; Interaction distances; Interaction length; Intermittent flows; Localized structures; Low frequency; Minimum distance; Perturbation frequency; Pipe walls; Spiral pattern; Turbulent intermittency

Journal Title:

Journal of Fluid Mechanics

Volume: 
681

ISSN:

14697645

Publisher:

Cambridge University Press

Date Published:

20110825

Start Page: 
193

End Page:

204

DOI: 
10.1017/jfm.2011.189

Open access: 
no 