Wake patterns of freely vibrating side-by-side circular cylinders in laminar flows

Wake patterns behind two freely vibrating circular cylinders in side-by-side arrangements are numerically investigated through two-dimensional computational fluid dynamics simulations. The two cylinders, with an equal diameter and a low mass ratio (the cylinder mass/the displaced fluid mass) of 2, can only oscillate in the transverse direction, and they are subject to the uniform laminar flows with the Reynolds number of 100. The center-to-center spacing over a cylinder diameter ratio (s/D) is varied from 2 to 5. For each s/D, the reduced velocity U-r (defined by U-infinity/f(n)D, where U-infinity is the free-stream velocity and f(n) is the cylinder natural frequency) is varied from 0 to 30. A small parametric increment of Delta U-r = 0.1 and Delta s/D = 0.1 is considered, providing a comprehensive analysis and insights into the wake patterns of the vortex shedding behind both cylinders. With more than 1500 new simulation cases, 8 distinctive wake patterns are identified through a map of U-r and s/D, with several well-defined boundaries governing different flow patterns. Qualitatively distinctive wake characteristics are analyzed through the evaluations of vortex dynamics, hydrodynamic lift/drag forces and cylinder vibration responses. (C) 2019 Elsevier Ltd. All rights reserved.