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Structure of Turbulent Vortices in a Compound Channel

Rimkus A.

Archives of Hydro-Engineering and Environmental Mechanics

2012

Vol. 59, nr 3-4

113-135

In spite of many investigations performed on turbulent flows, their structure has not yet been sufficiently explored. The difficulty is that, when a detailed picture of the velocity field is necessary, the widely employed Particle Image Velocity (PIV) method can provide photos covering only a short interval of flow, which cannot include the largest structures of turbulent flow, and consequently these structures cannot be investigated. In this study, the author tried to obtain necessary data about the processes occurring in the flow by analyzing instantaneous velocity measurements carried out by 3D means. A measurement at the points of a low cross-section takes at least 1 minute. During this time all vortex structures, including the largest, occur repeatedly many times and can be studied. The analysis of such measurements was the aim of this article. The process of the generation of vortices at the bottom and their further development, including the conditions of the development of the largest vortices, has been investigated. The results of these investigations are discussed in this article.

Effects of a fully submerged boulder within a boulder array on the mean and turbulent flow fields: Implications to bedload transport

Papanicolaou A., Kramer C., Tsakiris A., Stoesser T., Bomminayuni S., Chen Z.

Acta Geophysica

2012

Vol. 60, no. 6

1502-1546

The objective of this coupled experimental and numerical study is to provide insight into the mean and turbulent flow fields within an array of fully submerged, isolated, immobile boulders. Our study showed that the velocity defect law performed well for describing the mean flow around the boulder within the array. A prerequisite, however, was to accurately estimate the spatial variability of u* around the boulder, which was achieved via the boundary characteristics method. The u* exhibited considerable spatial variability within the array and form roughness was shown to be up to 2 times larger than the skin roughness in the boulder near-wake region. Because the boulders bear a significant amount of the flow shear, the available bed shear stress for entrainment of the mobile sediment, τols, near the boulders was roughly 50% lower than the ambient τols. The τols variability induced by the boulders could lead to a threefold overestimation of the sediment transport rate.