Analysis of Attack Angle Effect on Flow Characteristics Around Torpedo-Like Geometry Placed Near the Free-Surface via CFD

Abstract

In this study, the flow characteristics of torpedo-like geometry placed near the free-surface at various angles of attack were investigated numerically. The study was carried out at the Reynolds number of Re=4x104 between immersion ratios of 0.75≤h/D≤3.5 and angles of attack α=0°,4°, 8°, and 12°. Large Eddy Simulation (LES) turbulence model was used along with the Volume of Fluid (VOF) multiphase model to investigate the effects of free-surface. Wake region had an asymmetrical structure near the free-surface as a result of the interaction. A jet-like flow region was observed between the geometry and the free-surface at lower immersion ratios due to the restriction of the flow area. This flow region had a downward movement towards the lower pressure wake region. The drag coefficient, CD, values were increased with the decrease of immersion ratio. At angles of attack α=8° and 12°, the flow separation occurring near the nose caused an additional restriction in the flow area and directed the jet-like flow toward free-surface. Variation of Froude numbers (Fr) depending on the immersion ratio is examined, and it is found that Fr number and corresponding drag coefficient have higher values for the lower immersion ratio. The free-surface effect was found negligible at h/D≥2.5 for all cases.