Numerical Study on VIV Suppression and Drag Reduction by a Helical Grooved Cylinder

Abstract To understand the drag reduction and VIV suppression mechanisms of a cylinder with helical grooves, numerical studies by LES model have been carried out on a fixed cylinder to better investigate the flow patterns. The validation of the numerical models was completed by comparison of the numerical results with available experimental data. Flow characteristics of the cylinders with and without grooves were investigated in detail at Reynolds number of 9.0E+04 by a directly comparative approach. It was found that the mechanisms of VIV suppression by helical grooves are quite like those of helical strakes. Typical vortex coherence behind a smooth cylinder has been broken and vortex formation has been delayed due to the weaker interaction of the shear layers. The drag reduction of the cylinder with helical grooves is due to the recovery of the base pressure. There are similarities in drag reduction mechanisms between helical grooves and other small scale circumferential or longitudinal grooves, while the fundamental drag reduction mechanism of helical grooves can be more complex.