Abstract
The flow fields behind elliptic cylinders adjacent to a free surface were investigated experimentally in a circulating water channel. A range of cylinder aspect ratios (AR=2, 3, 4) were considered, while the cross-sectional area of the elliptical cylinder was kept constant. The main objective of this study was to investigate the effect of cylinder aspect ratio and a free surface on the flow structure in the near-wake behind elliptic cylinders. For each elliptic cylinder, the flow structure was analyzed for various values of the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV (Particle Image Velocimetry) system. For each experimental condition, 350 instantaneous velocity fields were obtained and ensemble-averaged to obtain the mean velocity field and spatial distribution of the mean vorticity statistics. The results show that near-wake can be classified into three typical flow patterns: formation of a Coanda flow, generation of substantial jet-like flow, and attachment of this jet flow to the free surface. The general flow structure observed behind the elliptic cylinders resembles the structure previously reported for a circular cylinder submerged near a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder differ from those observed for a circular cylinder. These trends are enhanced as cylinder aspect ratio is increased. In addition, the free surface distortion is also discussed in the paper.
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References
Choi JH, Lee SJ (2000) Ground effect of flow around an elliptic cylinder in a turbulent boundary layer. J Fluid Struct 14:697–709
Daichin, Lee SJ (2001) Flow structure of the wake behind an elliptic cylinder close to a free surface. KSME Int J 15(12):1784–1793
Gerrard JH (1966) The mechanics of the formation region of vortices behind bluff bodies. J Fluid Mech 25(2):401–413
Maruno E, Suzuki K, Sato T (1978) A turbulent boundary layer disturbed by a cylinder. J Fluid Mech 87:121-141
Maruno E, Suzuki K, Sato T (1985) Turbulent heat transfer in a flat plate boundary layer disturbed by a cylinder. Int J Heat Fluid Flow 6:241-248
Miyata H, Shikazono N, Kanai M (1990) Forces on a circular cylinder advancing steadily beneath the free-surface. Ocean Eng 17(1/2):81–104
Modi VJ, Dikshit AK (1975) Near wakes of elliptic cylinders in subcritcal flow. AIAA J 13:490–497
Modi VJ, Wiland E (1970) Unsteady aerodynamics of stationary elliptic cylinders in subcritical flow. AIAA J 8:1814–1821
Sheridan J, Lin JC, Rockwell D (1997) Flow past a cylinder close to a free surface. J Fluid Mech 33:1–30
Shin DS, Lee SJ (2000) Velocity field measurements of flow inside snout of continuous hot-dip galvanizing process using a single-frame PIV technique. ISIJ Int 40:484–490
Summer BM, Fredson J (1997) Hydrodynamics around cylindrical structures. World Scientific, New York (ISBN 981–02–3056)
Taniguchi S, Miyakoshi K (1990) Fluctuating fluid forces acting on a circular cylinder and interference with a plane wall. Exp Fluids 9:197–204
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This work was supported by the NRL (National Research Laboratory) program of the Ministry of Science and Technology, Korea.
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Daichin, ., Lee, S.J. Near-wake flow structure of elliptic cylinders close to a free surface: effect of cylinder aspect ratio. Exp Fluids 36, 748–758 (2004). https://doi.org/10.1007/s00348-003-0755-1
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DOI: https://doi.org/10.1007/s00348-003-0755-1