On the Formation Mechanisms of Artificially Generated High Reynolds Number Turbulent Boundary Layers
File(s)
Author(s)
Rodríguez-López, E
Bruce, PJK
Buxton, ORH
Type
Journal Article
Abstract
We investigate the evolution of an artificially thick turbulent boundary layer generated
by two families of small obstacles (divided into uniform and non-uniform wall normal
distributions of blockage). One- and two-point velocity measurements using constant temperature
anemometry show that the canonical behaviour of a boundary layer is recovered after
an adaptation region downstream of the trips presenting 150 % higher momentum thickness
(or equivalently, Reynolds number) than the natural case for the same downstream distance
(x ≈ 3 m). The effect of the degree of immersion of the trips for h/δ 1 is shown to play a
secondary role. The one-point diagnostic quantities used to assess the degree of recovery of
the canonical properties are the friction coefficient (representative of the inner motions), the
shape factor and wake parameter (representative of the wake regions); they provide a severe
test to be applied to artificially generated boundary layers. Simultaneous two-point velocity
measurements of both spanwise and wall-normal correlations and the modulation of inner
velocity by the outer structures show that there are two different formation mechanisms for
the boundary layer. The trips with high aspect ratio and uniform distributed blockage leave
the inner motions of the boundary layer relatively undisturbed, which subsequently drive
the mixing of the obstacles’ wake with the wall-bounded flow (wall-driven). In contrast, the
low aspect-ratio trips with non-uniform blockage destroy the inner structures, which are then
re-formed further downstream under the influence of the wake of the trips (wake-driven).
by two families of small obstacles (divided into uniform and non-uniform wall normal
distributions of blockage). One- and two-point velocity measurements using constant temperature
anemometry show that the canonical behaviour of a boundary layer is recovered after
an adaptation region downstream of the trips presenting 150 % higher momentum thickness
(or equivalently, Reynolds number) than the natural case for the same downstream distance
(x ≈ 3 m). The effect of the degree of immersion of the trips for h/δ 1 is shown to play a
secondary role. The one-point diagnostic quantities used to assess the degree of recovery of
the canonical properties are the friction coefficient (representative of the inner motions), the
shape factor and wake parameter (representative of the wake regions); they provide a severe
test to be applied to artificially generated boundary layers. Simultaneous two-point velocity
measurements of both spanwise and wall-normal correlations and the modulation of inner
velocity by the outer structures show that there are two different formation mechanisms for
the boundary layer. The trips with high aspect ratio and uniform distributed blockage leave
the inner motions of the boundary layer relatively undisturbed, which subsequently drive
the mixing of the obstacles’ wake with the wall-bounded flow (wall-driven). In contrast, the
low aspect-ratio trips with non-uniform blockage destroy the inner structures, which are then
re-formed further downstream under the influence of the wake of the trips (wake-driven).
Date Issued
2016-03-14
Date Acceptance
2016-02-16
Citation
Boundary-Layer Meteorology, 2016, 160 (2), pp.201-224
ISSN
0006-8314
Publisher
Springer
Start Page
201
End Page
224
Journal / Book Title
Boundary-Layer Meteorology
Volume
160
Issue
2
Copyright Statement
The final publication is available at Springer via http://dx.doi.org/10.1007/s10546-016-0139-8
Subjects
Meteorology & Atmospheric Sciences
0401 Atmospheric Sciences
Publication Status
Published