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

Bauri Krishna Pada

Acta Geophysica

2022

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.

Two-dimensional turbulent burst examination and angle ratio utilization to detect scouring/sedimentation around mid-channel bar

Khan Mohammad Amir, Sharma Nayan, Pu Jaan, Aamir Mohammad, Pandey Manish

Acta Geophysica

2021

Vol. 69, no. 4

1335--1348

River morphological dynamics are complex phenomena in natural and environmental fows. In particular, the sediment transport around braid mid-channel bars has not gained enough understanding from previous research. The efect of submergence ratio on the turbulence behavior in the proximity of the bar has been investigated in this study. The spatial distribution of turbulent fow in the proximity of bar has been studied by plotting the depth-averaged two-dimensional contours of turbulent kinetic energy. The high value of TKE has been observed in regions just downstream from the bar. It is due to the vortex shedding occurring in that region. The interaction of sweep and ejection events have been analyzed using the parameter Dominance Function obtained from the ratio of occurrence probability of ejection events to the occurrence probability of sweep events. This outcome indicates that the depth averaged parameter Dominance Function has successfully predicted the high scouring region which makes it an ideal parameter for analyzing the scour phenomena in real-world water management projects. The high scouring zone lies in the close proximity of the bar. This shows that the scouring efect from the bar is limited to its close region. The magnitude of scouring occurring at the upstream region of the bar also increases with the increment of submergence ratio. The relationship of quadrant event inclination angles with the sediment transport occurring in the proximity of bar has been also studied, where an Angle Ratio parameter has been utilized for linking the bed elevation change with the inclination angle. The results indicate that the AR parameter has been successfully tested in this study to show its competence to represent the turbulent burst-induced bed sedimentation and scouring.