Deflected oscillatory wake pattern behind two side-by-side circular cylinders

Wake flow behind structures is of fundamental significance and practical interest in ocean engineering. Several asymmetric flow patterns, such as the deflected stationary, flip-flop and deflected oscillatory wakes, behind two cylinders in a side-by-side arrangement have been reported most recently. In the present work, direct numerical simulations together with the state-of-art dynamic mode decomposition are used to reveal the underlying physics of deflected oscillatory wake pattern with low Reynolds number and intermediate gap ratio. Asymmetric flow structures are observed numerically in certain arrangements. Specially, the structure for gap flow is similar to that observed in flip-flop pattern induced by the secondary instability, but asymmetric here. It is found that the drag coefficient and lift coefficient under such circumstances are dominated by the asymmetric gap flow structure rather than the vortex street in the downstream. The present work provides a new scenario to the wake flow patterns behind two side-by-side cylinders with intermediate gap ratios, and it is potentially helpful in understanding the vibrating behaviors of adjacent cylinders.