Hydrodynamic force and vortex dynamics around an inclined cylinder in oscillatory flow

Abstract

Large eddy simulation is performed to investigate oscillatory flow around a circular cylinder at a Reynolds number of Re = 3900 under Keulegan–Carpenter numbers of KC = 15, 30, and 60 and inclination angles of α = 0°, 30°, 45°, and 60°. The validity of the independence principle (IP) is analyzed, and the contributions to drag and lift are quantified using the force partitioning method (FPM). The results indicate that the validity of IP expands significantly with increasing KC. At KC = 15, the inline drag coefficient is comparable only for α ≤ 30°, whereas at KC = 60, it remains nearly invariant up to α = 60°. This is because the longer stroke length at high KC allows vortices to fully develop within each half-cycle, producing more coherent primary wake structures and helping preserve quasi-two-dimensional flow characteristics even at large inclination angles. FPM reveals that the forces in both the x and y directions are highly correlated with the vortex-induced forces. Decomposition of the vortex force shows that the spanwise–vortex contribution dominates the drag and lift force. Moreover, as the inclination angle increases, the reduced normal velocity and enhanced axial velocity weaken near-cylinder vortex formation and promote axial stretching of vortices, thereby reducing vortex coherence and lowering the peak magnitudes of the vortex-induced forces.