Organised turbulence over mobile and immobile hydraulically rough boundaries

• Author(s): Leal, J. B. ; Ferreira, Rui M. L. ; Franca, Mário J. ; Cardoso, António H.
• Date: 2009
• Persistent ID: http://hdl.handle.net/10362/5046
• Origin: Repositório Institucional da UNL
• Subject(s): Turbulent coherent structures; Laser doppler anemometry; Mobile bed
• Document Type: Conference Object
• Language: English

Description

33rd IAHR Congress: Water Engineering for a Sustainable Environment The present work is aimed at the study of near-bed organised turbulence over mobile and immobile, porous, hydraulically rough boundaries. The bed was permeable and composed of non-cohesive sediments. Two data sets were analysed, characterised by the same u*. The mobile bed data featured generalised sediment transport for all size fractions smaller than the d90. The fixed bed was obtained as result of an armouring process. Comparison of these data sets reveals differences on such parameters of the bursting cycle as the maximum shear stress and the transported momentum. These results point to a reorganization of turbulence, in the near-bed region, when the bed is mobile. The impacts of these reorganization are discussed, namely in what concerns the third order moments of the distributions of the velocity fluctuations.