Abstract
This study concerns the evolution of flow field and hydrodynamic characteristics within the developing scour hole around a four-pile group with 2 × 2 arrangement. The instantaneous velocities in scour holes at four typical stages during the scouring process were measured by an acoustic Doppler velocimeter (ADV). The evolution and spatial distribution of the time-averaged flow field, turbulence, and the corresponding hydrodynamic characteristics within scour holes were compared. The time-averaged flow field shows that the reverse flow, downward flow, and horseshoe vortex are formed in the upstream of the pile group. During the scouring process, the mean components of flow characteristics (i.e., mean velocity, vorticity, and bed shear stress) around the pile group decrease while the fluctuating components (i.e., turbulence intensity) intensify simultaneously. Similarity of turbulence intensity profiles was found within different scour holes. The horseshoe vortex at upstream of each pile merges and the shear layer in the gap region extends when the dimension of the scour hole increases to that of equilibrium scour status, indicating that the four piles behave more like a single bluff body. With the development of scour holes, the large-scale horseshoe vortex system becomes more stable and the dissipation of small-scale eddies becomes more significant.
Highlights
Pile-group foundations are widely used in practice to support structures [1], such as bridges, offshore oil platforms, offshore wind power equipment, etc
We emphasize again that it is necessary to study the variations of flow fields and hydrodynamic characteristic with the development of scour holes to deepen our understanding of the scouring process around a pile group
By comparing the values of the distributed un between the two scour hole cases, it was evident that the magnitudes of un for the case of hs/he = 1 were generally less than the case of it was evident that the magnitudes of un for the case of hs /he = 1 were generally less than the case of hs/he = 4/7, both upstream and downstream of the pile group
Summary
Pile-group foundations are widely used in practice to support structures [1], such as bridges, offshore oil platforms, offshore wind power equipment, etc. Measured the flow field around a complex bridge pier (consisting of a pile cap and a 2 × 4 pile group), and analyzed the mean velocities, turbulence intensities, and Reynolds stresses at different horizontal and vertical planes; they mainly focused on the flow field in the upper region of the scour hole and ignored the flow field near the bottom of the scour hole as well as the gap between the piles. We emphasize again that it is necessary to study the variations of flow fields and hydrodynamic characteristic with the development of scour holes to deepen our understanding of the scouring process around a pile group. Is a first step for further exploring the mechanism of local scour around pile group
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