Numerical Study of Flow Features Around Submerged Circular and Square Piles at Flat and Scoured Beds Using OpenFOAM

Elucidating the flow features around piles in local scouring processes is crucial for studies of local scouring mechanisms and scour depth estimates. This study details the flow turbulence characteristics of two submerged piles that are determined by solving the Navier-Stokes equations with the improved delayed detached eddy simulation model. This model is verified by comparing experimental and numerical results for hydrodynamic parameters with the literature for both square-crossing piles (SCPs) and circular-crossing piles (CCPs). Original topographies of flat and scoured beds (i.e., the initial and equilibrium scouring stages) are based on experimental results obtained by the authors in the present paper. SCP and CCP flow features in the scouring process are discussed. The results indicate that during the scouring process, the time-averaged drag coefficient and root mean square (rms) of the lift coefficient increase linearly in the CCP test, while the rms of the lift coefficient in the SCP test decreases linearly. Moreover, the minimum pressure coefficient is always located in the upstream corners in the SCP case but moves from 72.5 degrees to 79.5 degrees when the scour hole is completely developed in the CCP case. Downward flow behind the pile, which is generated by separated boundary layers above the top face of the pile, can reach the sand bed and turn the separated shear layers into patches of small vortices in the near-wake regions. Thus, the high shear stress zones are mainly at the scour edges under scoured-bed conditions.