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Shallow Flow Visualization and Coherent Structures Around a Single Groyne

Author(s): Kadota Akihiro; Suzuki Koichi; Rummel Andreas Christof; Weitbrecht Volker; H. Jirka Gerhard

Linked Author(s): Volker Weitbrecht

Keywords: Groyne; Shallow flow; Particle tracking velocimetry (PTV); Proper orthogonal decomposition (POD); Conditional sampling analysis

Abstract: Groynes have been used for the stabilization of banks and for creating a navigation channel by confining the cross-sectional area, especially for large rivers world wide. One important characteristic of Japanese rivers is the sudden change of discharge due to heavy rainfalls so that the groynes change rapidly from submerged and emerged flow conditions. This phenomenon in one of the reasons for the scouring problem leading to the collapse of groynes as well as other man made structures. Therefore, the present study focuses the effects of submergence and emergence on instantaneous-coherent structures around a single groyne. To investigate the instantaneous flow patterns around a single groyne, a scale model was installed in the shallow water table and experiments were conducted by means of surface flow visualization technique. A particle tracking velocimetry (PTV) method has been developed for shallow flow conditions and has been adopted to estimate the instantaneous velocity fields to cope with the problem of a very high dynamic velocity range outside and inside of the dead zone behind the groyne. Proper orthogonal decomposition (POD) is applied to obtain an impression of the fluctuating flow pattern and its coherent structures. Conditional sampling analysis is also applied to reveal the advection properties of POD decomposed flow pattern. The paper discusses the differences in the mean and rms velocity profiles, POD decomposed coherent patterns and their advection properties under submerged and emerged conditions. One of main results is the distribution of coherent vortices generated at the groyne tip due to high shear forces in the mixing layer between main stream and dead zone.

DOI:

Year: 2007

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