Three-dimensional effects for flow past a wavy cylinder at low Reynolds numbers

The three-dimensional (3D) flow characteristics affected by the structural heterogeneity of a wavy cylinder varied sinusoidally along the spanwise direction at a low Reynolds number (50∼350), are studied using numerical simulations. Compared with a uniform cylinder, the transition routes and vortex shedding modes of a wavy cylinder can be revealed based on the Strouhal number–Reynolds number relationship, with new vortex structures features discovered in each mode. Unsynchronized transitions between several 3D shedding modes and the resulting hysteresis-like phenomenon attributed to different initial conditions. The extrinsic 3D effects caused by the structural wavy perturbations afford the inhomogeneous spanwise variations in flow physical quantities, such as the pressure coefficient, time-averaged separation angles, and vortex formation lengths. The effects of the Reynolds number on the wake quantities of the wavy cylinder are compared with those of a uniform cylinder, which is described by a single function form in the laminar regime and irregular features in the 3D wake-transition regime. In addition, the deviations of the time-averaged separation angles between the two-dimensional (2D) and 3D results are adopted to reveal the strengthened three-dimensionality of the flow for a wavy cylinder and its variations with shedding mode transitions.