Organized turbulence over mobile and immobile hydraulically rough boundaries

The present work is aimed at the study of near-bed organised turbulence over mobileand immobile, porous, hydraulically rough boundaries. The bed was permeable andcomposed of non-cohesive sediments. Two data sets were analysed, characterised bythe same u*. The mobile bed data featured generalised sediment transport for all sizefractions smaller than the d90. The fixed bed was obtained as result of an armouringprocess. Comparison of these data sets reveals differences on such parameters of thebursting cycle as the maximum shear stress and the transported momentum. Theseresults point to a reorganization of turbulence, in the near-bed region, when the bedis mobile. The impacts of these reorganization are discussed, namely in whatconcerns the third order moments of the distributions of the velocity fluctuations.