Loading...
Please wait, while we are loading the content...
Similar Documents
The rough favourable pressure gradient turbulent boundary layer
| Content Provider | Scilit |
|---|---|
| Author | Cal, Raúl Bayoán Brzek, Brian Johansson, T. Gunnar Castillo, Luciano |
| Copyright Year | 2009 |
| 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 $U_{∞}$ δ∗/δ scaling. Furthermore, when scaled with U^{2}$_{∞}$, the $〈u^{2}$〉 component of the Reynolds stress augments due to the rough surface despite the imposed favourable pressure gradient; when using the friction velocity scaling $u∗^{2}$, 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 $〈v^{2}$〉 and -〈uv〉 components for the $u∗^{2}$ or U_{∞}$^{2}$ scaling. These effects are reflected in the boundary layer parameter δ∗/δ, which increase due to roughness, but decrease due to the favourable pressure gradient. Additionally, the pressure parameter Λ 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 on the favourable pressure gradient condition and surface roughness. |
| Related Links | http://publications.lib.chalmers.se/records/fulltext/105271/local_105271.pdf https://www.cambridge.org/core/services/aop-cambridge-core/content/view/0908B0F32AE3A0B7C790BC8A1BCCDF41/S0022112009991352a.pdf/div-class-title-the-rough-favourable-pressure-gradient-turbulent-boundary-layer-div.pdf |
| Ending Page | 155 |
| Page Count | 27 |
| Starting Page | 129 |
| ISSN | 00221120 |
| e-ISSN | 14697645 |
| DOI | 10.1017/s0022112009991352 |
| Journal | Journal of Fluid Mechanics |
| Volume Number | 641 |
| Language | English |
| Publisher | Cambridge University Press (CUP) |
| Publisher Date | 2009-12-25 |
| Access Restriction | Open |
| Subject Keyword | Journal of Fluid Mechanics Fluids and Plasmas Physics Pressure Gradient Turbulent Boundary Layer |
| Content Type | Text |
| Resource Type | Article |
| Subject | Applied Mathematics Mechanics of Materials Condensed Matter Physics Mechanical Engineering |
