Numerical simulation of flows around two unyawed and yawed wavy cylinders in tandem arrangement

The turbulent flows around two fixed unyawed and yawed wavy cylinders in tandem arrangement at a subcritical Reynolds number of 3900 were studied using three-dimensional large eddy simulation. A range of spacing (L) between the cylinders from 1.5Dm to 5.5Dm with yaw angles of α=0°, 30° were investigated so as to identify the effects of cylinder spacing ratio and yaw angle as well as the coupling effects of the two wavy cylinders in tandem. The instantaneous near wake flow patterns around the cylinders were captured. Flows around circular cylinders with the same configurations were also obtained for comparison. The effects of the vortex shedding from the upstream cylinder on the fluid-dynamic forces acting on the downstream one were examined. Results show that vortex shedding behind the upstream wavy cylinder occurs at a further downstream position compared with that of the circular upstream cylinder. This leads to the weakening of the effect of bodies' vibration of the cylinders as well as an evident reduction of drag. With a yaw angle of 30°, the vortex formation lengths behind both the upstream and downstream cylinders decrease, typically for the wavy cylinders configuration. However, the effects of drag reduction and the control of bodies' vibration still exist except for the spacing ratio of L/Dm=3.5, which is in the critical spacing ratio regime for two wavy cylinders in tandem.

► We model the turbulent flows around two fixed unyawed and yawed wavy cylinders in tandem arrangement.
► We compare the results with two circular cylinders of the same configuration.
► We found that for a range of spacing between the tandem cylinders, drag and transverse force fluctuations are reduced by the addition of waviness along the cylinder span.
► We identify the optimal separation length between the two cylinders and when the principle of independence with respect to the yaw angle stays valid.