Steady-State Hydrodynamic Power Attenuation by Finned-Buoys

Results of experimental and computational fluid dynamics (CFD) studies conducted to compare the flow-energy-attenuating performances of two different buoy configurations are presented. A finned-body was experimentally studied in two orientations—one with a splitter and one in a 22.5 deg yaw orientation (with no splitter). The finned-buoy is designed for both wave and current attenuation; however, only the current application is discussed here. Scaled models were subjected to wind tunnel testing and CFD analyses. For this study, the steady-state drag coefficient (C_D) is considered to be the performance measure. The CFD model is used to match the physical testing by utilizing the k–ω turbulence model. Reynolds numbers (based on the tip-to-tip fin diameter) approaching the drag crisis are used to evaluate the bodies of interest, both of which have an aspect ratio (draft-to-diameter) of 1.85. The finned-bodies do encounter a drag crisis (as commonly seen with a cylinder), since the fins cause the buoys to act as a bluff body. The flow structures around the bodies are examined and compared to those predicted by established theories. For the finned-body, the 22.5 deg yaw orientation is found to have a consistently higher drag than the splitter orientation. The drag enhancement is explained by two phenomena. The first is a low-pressure area located in pockets adjacent to the upstream fins. The second is the absence of the drag-crisis, due to fixed separation points at the fin tips for all Reynolds numbers.