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基于涡量矩理论的绕振荡水翼涡动力学分析

VORTEX DYNAMICS OF A PITCHING HYDROFOIL BASED ON THE VORTICITY MOMENT THEORY

  • 摘要: 文章采用标准k-ω SST湍流模型和动网格技术, 实现了绕俯仰振荡NACA66水翼非定常流动结构与水动力特性的数值模拟, 并基于有限域涡量矩理论定量表征了局部旋涡结构对水翼动力特性的影响. 研究结果表明: 在水翼升程阶段, 当攻角较小时, 层流向湍流的转捩点由水翼尾缘向前缘移动; 在较大攻角时, 顺时针尾缘涡−TEV在水翼吸力面上生成并向前缘发展, 同时与吸力面上的顺时针前缘涡−LEV融合发展为附着在整个吸力面上的新前缘涡−LEV, 新的−LEV与逆时针尾缘涡+TEV相互作用直至完全脱落, 直接导致了水翼的动力失速, 在回程阶段, 绕振荡水翼的流场结构逐渐由湍流转变为层流. 基于有限域涡量矩理论的定量分析发现, 有限域内附着的−LEV和−TEV提供正升力, 当−LEV发展覆盖整个吸力面时对升力的贡献最大, 占总升力近50%, 而+TEV提供负升力. 同时发现, 有限域内各旋涡内部的不同区域提供的升力有正有负; 而逸出有限域的旋涡内部不同区域提供的升力方向均保持一致, 其中顺时针涡提供正升力, 而逆时针涡提供负升力. 在失速阶段, 域外旋涡整体对升力贡献较小且存在小幅波动, 体现了流动的非定常性.

     

    Abstract: In this paper, the unsteady vortical structures and corresponding hydrodynamic characteristics of the pitching NACA66 hydrofoil are numerically simulated with the standard k-ω SST turbulence model and dynamic mesh technology. And the influence of local vortical structures on the transient lift is quantitatively obtained based on the finite-domain vorticity moment theory. The results show that during the upstroke stage, transition of laminar flow to turbulence moves from the trailing edge to the leading edge of the hydrofoil at small angle of attack. At relatively higher angle of attack, a clockwise trailing edge vortex ( defined as −TEV)appears on the suction surface firstly. It gradually increases in size and develops towards the leading edge to be fused with the clockwise leading edge vortex (defined as −LEV) there. Then the new developed −LEV interacts with the counterclockwise trailing edge vortex (defined as +TEV) until it falls off completely, which directly leads to the dynamic stall of the hydrofoil. Meanwhile, quantitative analysis based on the finite-domain vorticity moment theory shows that the attached −LEV and −TEV in the finite domain provide positive lift, while +TEV provides negative lift. At the moment when −LEV covers almost the whole suction surface, it contributes the most to the transient total lift which accounts for about 50%. It is also found that different parts of a vortex provide positive or negative lift. As for shedding vortices escaping from the finite domain, all regions of a vortex provide only consistent contribution instead, which means that a clockwise vortex provides positive lift, while a counterclockwise vortex provides negative lift. During the fluctuating stall stage, the overall contribution from the vortices out of the finite domain is quite little and has slight fluctuation, which reflects the unsteady characteristics of the vortical flow caused by the shedding and convection of large-scale vortices

     

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