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2 Acta Geophysica

2 2022

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Coherent structures around submerged circular and square cylinders due to change of orientation angle in steady current over plane bed

100%

Bauri K. P.

Acta Geophysica

2022

tom Vol. 70, no 5

2223--2250

The investigation of the bursting process and coherent structures around circular and square cylindrical structures for various angular alignments over a rigid plane bed are introduced. The coherent structures and shear stresses perform a substantial characteristic in bed particle entrainment and transport from the bed around these structures. Hence, bed shear stress, power spectra are determined from the measured velocity data, in addition, third-order correlation, turbulence intensity, and kinetic energy were investigated using quadrant analysis to explore the correlation between coherent structures and sediment movement. Turbulent coherent structures due to the variations of submergence depth, velocity, orientation angle of the square cylinder, and cylinder size are also investigated. Further, the measured velocity data using Acoustic Doppler Velocimeter were validated with numerical simulations using COMSOL Multiphysics 5.0 with k-ω turbulence closure model. Outcomes indicate that the wake zone length rises with the rise of submergence ratio for the square cylinder with different angular alignments than the circular and square cylindrical structures. Bed shear stress is higher for the square cylinder with different angular alignments than the circular cylinder. The wake vortex strength increases with angular alignment signifying excessive movement of bed sediments from the bed around the cylindrical structures. The interaction events predominate near the bed and middle height of the cylinder, whereas ejection and sweep events dominate far away from the bottom toward the top of the cylinders. The stress fraction is maximum for square cylinders with higher alignment angles.

Flow structure investigation over a pool-rife sequence in a variable width river

100%

Tabarestani E. S. , Afzalimehr H. , Pham Q. B.

Acta Geophysica

2022

tom Vol. 70, no 2

713--727

A comprehensive overview of flow characteristics in natural channels with bedforms is a vital issue in river management projects. Pool-rife sequences as common bedforms in the gravel-bed rivers significantly impact flow characteristics and turbulence intensity. The present study was taken by field investigation in the Babolroud River, Iran. A 95 m reach with variable width was chosen in this river and velocity components and shear stress were obtained in different sections. Quadrant analysis was also applied to determine the dominant bursting event in the pool section. The results revealed a phase shift for stream-wise velocity, near-bed velocities, and bed shear stress versus bed profile. In the pool, vertical velocity components were oriented downward near the bed and upward near the water surface, while in the rife section vectors were oriented towards the bed. The findings of quadrant analysis demonstrated the ejections and sweeps as a dominant event close to the bed and water surface, respectively.