Two-dimensional and three-dimensional simulations of oscillatory flow around a circular cylinder

Oscillatory flow around a cylinder is simulated using both two- and three-dimensional finite element models at Re¼2000 and KC¼1, 2, 5, 10, 17.5, 20 and 26.2. The same finite element method is used in both the two- and three-dimensional models. The purpose of this study is to investigate the feasibility of a two-dimensional model for simulating a three-dimensional flow in terms of fundamental flow characteristics and hydrodynamic forces. The vortex structures predicted by the two-dimensional model agree qualitatively with those by the three-dimensional model for the flow conditions where strong correlations exist along the span-wise direction (KC=10, 17.5 and 26.2). Three vortex shedding modes are reproduced by both two- and three-dimensional models at KC=20, which is close to the critical KC number between double-and three-pair regimes. The time histories of hydrodynamic force predicted by the two models agree with each other at KC=20. The predicted Morison force coefficients by the two-dimensional model are within 18% different from those predicted using the three-dimensional model for most of the cases. The two-dimensional model captures the majority of the genuine flow structures and hydrodynamic loads of a circular cylinder in an oscillatory flow.