Characteristics of flow in the wake region of a bluff vertical cylinder in the presence of waves,currents and combined wave-current flows.

Abstract

The presence of beat phenomena in the flow fields around a bluff cylinder in combined wave-current environments has been investigated through a hybrid approach comprising tow experiments and CFD simulations. A low vibration towing system has been specially designed and built to facilitate the flow measurements, wave measurements, flow visualization, and measurements of forces on a slender cylinder downstream of the bluff cylinder. Numerical simulations are carried out using STAR CCM+, based on DES-VOF. This study is conducted for different wave current combinations and the results reveal the presence of amplitude modulated signatures for flows of low KC numbers, at current wave velocity ratios (Uc/Uw) between 0.8 to 2.8 and wave KC numbers ranging from 0.25 to 0.50. The study shows that the beat phenomenon is associated with the interaction between the combined flow with the upstream bluff cylinder, resulting in amplitude modulation in the velocities, wave elevation and force signatures.