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Method for analyzing friction reduction effects of bubbles in friction-reducing ship
Method for analyzing friction reduction effects of bubbles in friction-reducing ship
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机译:分析减摩船中气泡减摩效果的方法
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摘要
A method is provided for analyzing the effects of bubbles on skin-friction reduction in a ship cruising in a bubbly flow field. A shear stress decrement t produced by a bubble in a flow field is obtained in a high frequency band region, in which a product of a bubble time-constant T and a turbulence frequency L in a flow field is sufficiently greater than 1, based on a resistive force Rv acting on a bubble derived from the bubble movements in a fluid flow direction along a ship surface and in a direction at right angles to a ship wall surface. Assuming that the shear stress a decrement is generated by a decrease in a gas mixing length, an expression for the operative wall constant 1 for bubbly flow including a parametric bubble diameter db is derived. Based on an expression relating the operative wall constant 1 and a local friction factor Cf in bubbly flow, and an expression relating the normal wall constant in non-bubbly flow and a local friction factor Cf0 in non-bubbly flow, an analytical solution is obtained for a skin-friction ratio Cf/Cf0.
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机译:提供了一种用于分析气泡在气泡流域中巡航的船舶上减少皮肤摩擦的影响的方法。由气泡在流场中产生的剪切应力减量 t Sub>在高频段区域获得,在该频段中,气泡时间常数T和湍流频率 L 基于作用在气泡上的阻力R v Sub>,气泡中的Sub>流场充分大于1,该阻力源自气泡沿船体表面在流体流动方向和向右方向上的运动与船壁表面的角度。假定剪切应力通过气体混合长度的减小而减小,那么对于气泡流动的有效壁常数 1 Sub>的表达式包括参数气泡直径d b Sub>派生。基于与气泡流动中有效壁常数 1 Sub>和局部摩擦系数C f Sub>相关的表达式,以及与非气泡流动中正常壁常数和相关的表达式相关的表达式非气泡流动中的局部摩擦系数C f0 Sub>,获得了皮肤摩擦比C f Sub> / C f0 Sub>的解析解。
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