---
res:
bibo_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 well-defined 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 well-defined link between
the Blasius and the Hagen-Poiseuille 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.@eng
bibo_authorlist:
- foaf_Person:
foaf_givenName: Devranjan
foaf_name: Samanta, Devranjan
foaf_surname: Samanta
- foaf_Person:
foaf_givenName: Alberto
foaf_name: de Lózar, Alberto
foaf_surname: De Lózar
- foaf_Person:
foaf_givenName: Björn
foaf_name: Björn Hof
foaf_surname: Hof
foaf_workInfoHomepage: http://www.librecat.org/personId=3A374330-F248-11E8-B48F-1D18A9856A87
orcid: 0000-0003-2057-2754
bibo_doi: 10.1017/jfm.2011.189
bibo_volume: 681
dct_date: 2011^xs_gYear
dct_publisher: Cambridge University Press@
dct_title: Experimental investigation of laminar turbulent intermittency in pipe
flow@
...