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An Experimental Study on Resistance Properties of an Asymmetrical Bottom Roughness in Oscillatory Flows

Author(s): H. Oshikawa; T. Komatsu; T. Shibata

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Keywords: Residual hydrodynamic force; Oscillatory flow; Submerged asymmetrical roughnessKeulegan-Carpenter number

Abstract: The characteristics of hydrodynamic forces on a submerged asymmetrical roughness, known as BANK block in oscillatory flows were experimentally investigated. In this study, a quarter sphere or half cylinder is used as a BANK block which is set on the bottom of channel with an angle of attack θ to an oscillating flow direction. Residual hydrodynamic force on a quarter sphere is based on hydrodynamic force in the range of normalized time t/T=0.7 to 1.15 (=0.15). Residual hydrodynamic force on a half cylinder is much larger than that on a quarter sphere due to the fact that the substantial length of a quarter sphere is smaller than that of a half cylinder. Furthermore, residual hydrodynamic force on a BANK block is almost constant with the change of θ when the Keulegan-Carpenter number (KC) is small. However, if KC is large, the force on a quarter sphere decreases with the increase of θ because residual lift force decreases in the range of θ = 50 to 90deg.


Year: 2003

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