Computational Fluid Dynamics Simulations of a Near-Wall Rectangular Cylinder in an Oscillatory Flow

In this study, the oscillatory flow around a near-wall rectangular cylinder at various KC values and gaps relative to the plane-wall boundary was explored using computational fluid dynamics (CFD) simulations. The numerical models were validated through comparison with experimental data for near-wall circular and square cylinders in oscillatory flow. Reasonable agreement was achieved between the numerical and experimental results for both cylindrical shapes. The variations in the flow field characteristics (velocity, vorticity, and pressure distribution) were examined over a single oscillation period. The in-line and lift coefficients (Cd,Cl) and Morison coefficients (CD,Cm) were calculated and discussed in relation to the flow field variations. It was demonstrated that as KC increased, the flow field became increasingly asymmetric at the upper and lower surfaces, accompanied by an increase in Clmax/Cdmax. For cylinders at a small distance from the plane wall (e/D=0.1), a significant increase in Cm was observed with increasing KC, a trend notably distinct from that observed in cases with larger gaps. Additionally, the correlation between vortex shedding (quantified by the Strouhal number, St), KC, and the gap ratio was investigated. Our findings reveal that the wall effects significantly compress the wall-side vortices.