- Title
- A turbulent boundary layer over a two-dimensional rough wall
- Creator
- Djenidi, Lyazid; Antonia, Robert A.; Amielh, Muriel; Anselmet, Fabien
- Relation
- Experiments in Fluids Vol. 44, Issue 1, p. 37-47
- Publisher Link
- http://dx.doi.org/10.1007/s00348-007-0372-5
- Publisher
- Springer
- Resource Type
- journal article
- Date
- 2008
- 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.
- Subject
- particle image velocimetry (PIV); planar laser induced fluorescence (PLIF); boundary layer; wall roughness; turbulence production
- Identifier
- http://hdl.handle.net/1959.13/41303
- Identifier
- uon:4722
- Identifier
- ISSN:0723-4864
- Language
- eng
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