基于负压梯度翼型栅格翼设计与水中数值分析

Design and Underwater Numerical Analysis of Grid Fins Based on Negative Pressure Gradient Foils

为改善栅格翼的水动力性能,基于流动不分离理论设计了负压梯度翼型,并将其运用于栅格翼的设计;数值模拟研究了该翼型与NACA0015翼型在一定的空化数和攻角条件下的升阻及压力分布特性;探究了3种叶片间距的负压梯度翼型栅格翼在不同攻角下的升阻、压力及空泡几何形状。结果表明,含攻角时,该翼型对应的临界空化数要比NACA0015的小,但二者升阻系数基本一致;小攻角情况下,栅格翼叶片数量增加时升力会趋于一常值,但阻力会不断增加;大攻角情况下,叶片数量的增加会导致升力和阻力均明显增加。对于同一叶片间距的栅格翼,攻角越大,栅格翼叶片由上至下空泡的长度和厚度减小的速率越大。对于不同叶片间距的栅格翼,叶片数量越大,各个叶片的压力干扰越剧烈,压差阻力越大,导致升阻比降低。同时,剧烈的压力干扰会导致栅格翼的空泡长度增加。因此,在满足水动力特性要求时,基于该文翼型设计负压梯度翼型栅格翼应尽量减少叶片数量。

To improve the hydrodynamic characteristics of grid fins,the negative pressure gradient foil was designed and applied to the grid fins based on the theory of unseparated flow.The lift-drag characteristics and pressure distribution of that foil and NACA0015 under certain cavitation number and angle of attack were numerically investigated.The lift-drag characteristics,pressure distribution,and the cavity geometry of the grid fins based on negative pressure gradient foil with three kinds of blade spacing at different attack angles were investigated.The results indicate that the critical cavitation number corresponding to the negative pressure gradient foil is smaller than that of NACA0015 when the angle of attack is included,but the lift-drag coefficients of them are basically the same.When the number of blades increases of the grid fins,the lift will tend to a constant value,but the resistance will continue to increase under the small attack angle.In the case of a large attack angle,the increase in the number of blades will lead to a significant increase in both lift and drag.For grid fins with the same blade spacing,the greater the angle of attack,the greater the decrease rate of the length and thickness of the cavity from the top blade to the bottom blade of grid fins.For grid fins with different blade spacing,the greater the number of blades,the more intense the pressure interference of each blade,and the greater the pressure drag,leading to worse lift-drag characteristics.And the severe pressure interference will lead to a longer cavity geometry of grid fins.Therefore,when meeting the requirements of hydrodynamic characteristics,the number of blades should be reduced as far as possible in the design of grid fins based on negative pressure gradient foil.