Wake stabilization mechanism of low-drag suppression devices for vortex-induced vibration

Inspired by the drag reduction mechanism in a tandem cylinder arrangement, the objective of this study is to numerically investigate the characteristic response of shear layer reattachment for the suppression of vortex-induced vibration (VIV). A new device termed as connected-C is introduced, whereby its geometry can be constructed by attaching a C-shaped foil at the end of a splitter plate behind a circular cylinder. We investigate the significance of each part of the connected-C device and compare the proposed device with conventional fairings, the splitter plate, and one of its variant disconnected-C device without the connector plate between the main cylinder and the C-shaped foil. To simplify the numerical study and to concentrate on the wake stabilization mechanism, the cylinder-device systems are only allowed to move in the transverse direction. There is no relative rotation between the cylinder and the attached devices. Two- and three-dimensional studies are carried out at low Reynolds number Re=100 and subcritical Reynolds numbers Re∈[6150,7400]. We observe the counter-rotating pair of recirculations and the shear layer reattachment for the vibrating connected-C device. These flow characteristics of the connected-C device result into a similar VIV performance as the fairing with respect to the suppression of VIV. Similar to fairings, there is a net reduction in the total drag force exerted over the combined cylinder-device system. Based on the results from the low Reynolds number study, while the presence of C-shaped device is essential to prevent the occurrence of galloping at high reduced velocity, the presence of connector plate is not necessary to suppress VIV.