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Analysis of the Flow Structure in a Side Open Channel Cavity of Aspect Ratio 1

Author(s): Motasem Darwish; Wernherbrevis; Yarko Nino

Linked Author(s): Yarko Niño

Keywords: Submerged Flow; Side open cavity; PIV; POD

Abstract: Many features in open channel flows, such as river harbours and fluvial dead arms, can be modelled as side cavities. The presence of these features can have a major effect on the characteristics of the fluvial hydrodynamics, sediment transport and on the dynamic of aquatic ecological system. The flow within a cavity is highly dependent on its geometrical characteristics and flow regime. In case of rectangular cavities, the most important geometrical parameter is the so-called aspect ratio (λ=L/W), which is the relation between the streamwise (W) and spanwise (L) lengths of the cavity. The cavity can have emerged flow conditions or submerged ones. Unlike the emerged flow condition, little is known about the flow during submerged circumstances, which can occur, for instance, during flooding events. This paper presents the analysis of Particle Image Velocimetry (PIV) measurements of a laboratory cavity ofλ=1. These measurements were obtained at three horizontal planes for four flow depths, which simulate different submergence scenarios. The analysis is focused on the description of flow patterns, Reynolds stresses and coherent structures obtained after a proper orthogonal decomposition (POD) of the two-dimensional time series. The results showed that the flow structure depends on the relation between the vertical dimension of the cavity and water depth in the floodplain. Furthermore, it is evident that low energy coherent structures occur during high flow depths. Finally, the local role of a lateral shear layer was shown to have a negligible influence on the structure at higher measurement planes, for most of the analysed submergence levels.


Year: 2013

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