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    Analysis of attack angle effect on flow characteristics around torpedo-like geometry placed near the free-surface via CFD
    (2021) Kılavuz, Alpaslan; Ozgoren, Muammer; Durhasan, Tahir; Sahın, Besir; Kavurmacıoglu, Levent Ali; Akıllı, Huseyin; Sarıgıguzel, Fuad
    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 ?=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 lowerpressure wake region. The drag coefficient, CD, values were increased with the decrease of immersion ratio. At angles of attack ?=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.
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    Öğe
    POD Analysis of Flow around Torpedo-Like Geometry with a Hemispherical Nose
    (2023) Kenan, Ömer; Yanıktepe, Bülent; Sekeroglu, Ertugrul; Ozgoren, Muammer; Akbudak, Ezgi; Durhasan, Tahir; Kılavuz, Alpaslan
    There has been an increased interest in underwater vehicles for a wide range of applications over the past decade. In the current study, flow characteristics around a common, torpedo-like geometry with a Myring profile were investigated at a length-based Reynolds number of Re=20000 using the Particle Image Velocimetry (PIV). As a result of PIV and Proper Orthogonal Decomposition (POD) analyzes in this study; instantaneous streamline topology ?, instantaneous vorticity ?L?U_? contours, instantaneous streamwise velocity component u?U_? graphs, cross-streamwise velocity component v?U_? graphs, instantaneous vorticity ?L?U_? graphs, perpendicular to the flow direction, instantaneous vortex graphs and time-averaged TKE graphs were evaluated and compared. At the same time, as a result of PIV analysis, time-average streamline topology <?> and Time-averaged vorticity <?L?U_? > contours values are given. When the flow characteristics were compared by using the obtained POD method of the PIV results, it was determined that although the POD data were generally quite similar to the PIV results, the POD analysis results had a more uniform flow structure and vortex turbulence was lessened.