The impacts of the free-surface and angle of attack on the flow structures around a torpedo-like geometry

• Published in: European journal of mechanics, B, Fluids B, Fluids, 2022-03, Vol.92, p.226-243
• Main Authors: Kilavuz, A., Sarigiguzel, F., Ozgoren, M., Durhasan, T., Sahin, B., Kavurmacioglu, L.A., Akilli, H., Sekeroglu, E., Yaniktepe, B.
• Format: Article
• Language: English
• Subjects: AUV; Flow separation; Free-surface; PIV; Turbulent flow; Vortical flow
• ISSN: 0997-7546; 1873-7390
• DOI: 10.1016/j.euromechflu.2021.12.005

This study presents the hydrodynamic characteristics around a torpedo-like geometry under the free-surface effect at different angles of attack using preliminary dye visualization and Particle Image Velocimetry (PIV). The optimized torpedo-like geometry is placed at submersion ratios between 0.5≤h/D≤3.50 where h is the distance to the free-surface from its centerline and D is the diameter. Throughout the experiments, angles of attack were taken as 0°≤α≤12° for two Reynolds numbers, Re = 2.0 × 104 and 4.0 × 104. The PIV method provided instantaneous vorticity and time-averaged velocity components, vorticity, streamline topology, fluctuating velocity components, Reynolds stress correlation, and the turbulent kinetic energy. This study focused on the stern section and the wake structures at h/D=1.0 . It is demonstrated that a jet-like flow region occurred between the model and the free-surface for all angles of attack at small submersion ratios of 0.5≤h/D≤1.0 while it is observed at h/D=1.5 for α=8°, a jet-like flow region occurred between the model and the free-surface. The impact of the jet-like flow was more noticeable for α=4° and 8° with velocity fluctuations in lower magnitudes. The nose section partially pierced the free-surface for h/D = 0.5, 0.75, and 1.0 in the range of 4°≤α≤12° and it prevented the wake region from connecting with the free-surface by directing the separated flow region toward the stern section. Pointwise variations of the turbulence data extracted from vertical lines within the wake region for all cases revealed that the effect of the free-surface on the turbulence statistics was negligible beyond h/D=2.0. [Display omitted] •The flow structures around torpedo like geometry were examined for 0°≤α≤12°, Re = 20 × 103 and 40 × 103.•Asymmetrical flow occurs at small submersion ratios of 0.5≤h/D≤1.0 while becoming nearly symmetrical for h/D = 3.5.•Pointwise variations of the turbulence data are helpful for validation and readers.•The critical point becomes closer to the trailing edge with increasing Reynolds number.•Characteristics of velocity fluctuations are greatly influenced by the free-surface.