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Power-law velocity profile in turbulent boundary layers: An integral reynolds-number dependent solution

100%

Castro-Orgaz O. , Dey S.

Acta Geophysica

2011

tom Vol. 59, no. 5

993-1012

Geophysical flows of practical interest encompass turbulent boundary layer flows. The velocity profile in turbulent flows is generally described by a log- or a power-law applicable to certain zones of the boundary layer, or by wall-wake law for the entire zone of the boundary layer. In this study, a novel theory is proposed from which the power-law velocity profile is obtained for the turbulent boundary layer flow. The new power-law profile is based on the conservation of mass and the skin friction within the boundary layer. From the proposed theory, analytical expressions for the power-law velocity profile are presented, and their Reynolds-number dependency is highlighted. The velocity profile, skin friction coefficient and boundary layer thickness obtained from the proposed theory are validated by the reliable experimental data for zero-pressure gradient turbulent boundary layers. The expressions for Reynolds shear stress and eddy viscosity distributions across the boundary layer are also obtained and validated by the experimental data.

Flow Characteristics over a Gravel Bedform: Kaj River Case Study

86%

Maddahi M. R. , Afzalimehr H. , Rowiński P. M.

Acta Geophysica

2016

tom Vol. 64, no. 5

1779--1796

The present study deals with the turbulence structure in order to better understand the interaction of bedform and flow characteristics in a gravel-bed river. Data measured above a bedform is used to analyze the importance of coherent structures in turbulent transfer. The Reynolds stress and turbulence intensity in stream-wise direction illustrate significant difference along the bedform, showing a three-layer distribution at the crest and a convex one at the downstream of bedform. Quadrant analysis technique is used to picture momentum exchange above the considered bedform and to find the dominant event in bursting process of the gravel bedform. Quadrant analysis demonstrates that the mechanisms of bedforms generation in sand and gravel-bed rivers are similar and sweep is the dominant event in both rivers.