Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/41303

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Title
A turbulent boundary layer over a two-dimensional rough wall
Author/Creator
Djenidi, Lyazid;  Antonia, Robert A.;  Amielh, Muriel;  Anselmet, Fabien
Institution
The University of Newcastle. Faculty of Engineering & Built Environment, School of Engineering
Description
Particle image velocimetry (PIV) measurements and planar laser induced fluorescence (PLIF) visualizations have been made in a turbulent boundary layer over a rough wall. The wall roughness consisted of square bars placed transversely to the flow at a pitch to height ratio of λ/k = 11 for the PLIF experiments and λ/k = 8 and 16 for the PIV measurements. The ratio between the boundary layer thickness and the roughness height k/δ was about 20 for the PLIF and 38 for the PIV. Both the PLIF and PIV data showed that the near-wall region of the flow was populated by unstable quasi-coherent structures which could be associated to shear layers originating at the trailing edge of the roughness elements. The streamwise mean velocity profile presented a downward shift which varied marginally between the two cases of λ/k, in agreement with previous measurements and DNS results. The data indicated that the Reynolds stresses normalized by the wall units are higher for the case λ/k = 16 than those for λ/k = 8 in the outer region of the flow, suggesting that the roughness density effects could be felt well beyond the near-wall region of the flow. As expected the roughness disturbed dramatically the sublayer which in turn altered the turbulence production mechanism. The turbulence production is maximum at a distance of about 0.5k above the roughness elements. When normalized by the wall units, the turbulence production is found to be smaller than that of a smooth wall. It is argued that the production of turbulence is correlated with the form drag.
Relation
Experiments in Fluids Vol. 44, Issue 1, p. 37-47
Publisher Link
http://dx.doi.org/10.1007/s00348-007-0372-5
Date
2008
Publisher
Springer
Keyword(s)
particle image velocimetry (PIV);  planar laser induced fluorescence (PLIF);  boundary layer;  wall roughness;  turbulence production
Resource Type
journal article
Identifier
http://hdl.handle.net/1959.13/41303
Identifier
ISSN:0723-4864
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Subject
"Experiments in Fluids"
 
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