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- Brzek, Brian, et al.
(författare)
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Near Wall Measurements in Rough Surface Turbulent Boundary Layers
- 2007
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Ingår i: J.M.L.M. Palma and A. Silva Lopes (Eds.), "Advances in Turbulence XI", Proceedings of the 11th EUROMECH European Turbulence Conference, June 25-28, 2007, Porto, Portugal. Springer proceedings in physics 117.. - 0930-8989. - 9783540726036 ; , s. 295-297
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Konferensbidrag (refereegranskat)
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- Cal, Raúl Bayoán, et al.
(författare)
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Benefits of a graduate international program
- 2005
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Ingår i: 6th International conference on Information technology based higher education and training, Santo Domingo, July 7-9, 2005.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Cal, Raúl Bayoán, et al.
(författare)
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Influence of external conditions on transitionally rough favorable pressure gradient turbulent boundary layers
- 2008
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Ingår i: Journal of Turbulence. - : Informa UK Limited. - 1468-5248. ; 9:38, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler anemometry measurements are carried out in order to investigate the influences of the external conditions on a transitionally rough favorable pressure gradient turbulent boundary layer. The acquired data is normalized using the scalings obtained by the meansof equilibrium similarity of the outer flow. The point at hand is to not only understand the interaction between the rough surface and the outer flow but also to include the external pressure gradient as the flow evolves in the streamwise direction. It is found that the velocityprofiles show the effects of the upstream conditions imposed on the flow when normalized withthe free-stream velocity. However, the profiles do collapse when normalized with U∞δ∗/δ,demonstrating that this scaling absorbs the roughness effects and upstream conditions. An augmentation in the Reynolds stresses occurs with an increase in the roughness parameter and a decrease due to the external favorable pressure gradient. However, close to the wall, thereis an increase due to the favorable pressure gradient while on the outer part of the boundarylayer there is a decrease in magnitude due to this imposed effect. The near-wall peak of the(u2) component is dampened by the surface roughness condition due to the destruction of theviscous sublayer. In addition, the shape of the profile in the inner region tends to flatten dueto the surface roughness. The upstream wind-tunnel speed also plays an important role thuscreating a Reynolds number dependence on the outer flow of the Reynolds stress components.Furthermore, through 11 consecutive downstream locations, the skin friction coefficient isobtained for smooth and rough favorable pressure gradient data. The skin friction showsdependencies on the Reynolds number, the roughness parameter, and the favorable pressuregradient condition in the transitionally rough regime; while for the fully rough regime, itbecomes form drag and the dependencies are on the favorable pressure gradient and theReynolds shear stress. The external condition effects are isolated with a fixed parametercomparison. Favorable pressure gradient effects slow down the growth of the boundary layerwhile the surface roughness promotes its growth.
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- Cal, Raúl Bayoán, et al.
(författare)
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The rough favourable pressure gradient turbulent boundary layer
- 2009
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Ingår i: Journal of Fluid Mechanics. - 0022-1120 .- 1469-7645. ; 641, s. 129-155
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler anemometry measurements of the mean velocity and Reynolds stresses are carried Out for a rough-surface favourable pressure gradient turbulent boundary layer. The experimental data is compared with smooth favourable pressure gradient and rough zero-pressure gradient data. The velocity and Reynolds stress profiles are normalized using various scalings Such as the friction velocity and free stream velocity. In the velocity profiles, the effects of roughness are removed when using the friction velocity. The effects of pressure gradient are not absorbed. When using the free stream velocity, the scaling is more effective absorbing the pressure gradient effects. However, the effects of roughness are almost removed, while the effects of pressure gradient are still observed on the outer flow, when the mean deficit velocity profiles are normalized by the U(infinity)delta(*)/delta scaling. Furthermore, when scaled with U(infinity)(2), the component of the Reynolds stress augments due to the rough Surface despite the imposed favourable pressure gradient; when using the friction velocity scaling it u(*)(2), it is dampened. It becomes 'flatter' in the inner region mainly due to the rough Surface, which destroys the coherent structures of the flow and promotes isotropy. Similarly, the pressure gradient imposed on the flow decreases the magnitude of the Reynolds stress profiles especially on the and - components for the u(*)(2) or U(infinity)(2) scaling. These effects are reflected in the boundary layer parameter delta(*)/delta, which increase due to roughness, but decrease due to the favourable pressure gradient. Additionally, the pressure parameter Lambda found not to be in equilibrium, describes the development of the turbulent boundary layer, with no influence of the roughness linked to this parameter. These measurements are the first with an extensive number of downstream locations (11). This makes it possible to compute the required x-dependence for the production term and the wall shear stress from the full integrated boundary layer equation. The finding indicates that the skin friction coefficient depends oil the favourable pressure gradient condition and surface roughness.
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