重叠网格技术下振荡水翼的水动力特性

Hydrodynamic performance of oscillating hydrofoils based on overset grid technique

摘要:

为研究运动参数对于振荡水翼在潮流中获能效率的影响,给出水翼高获能效率时的运动参数分布规律,提高振荡翼式潮流能发电装置的获能效率。基于重叠网格技术建立了振荡水翼的数值计算模型,并对网格的有效性进行了验证,通过改变水翼的折算频率f*、摆角幅值θ₀、升沉振幅h₀等运动参数,对二维振荡水翼的水动力特性及相应的获能效率进行了研究,分析了涡脱落对水翼运动过程中获能效率的影响；同时研究了双翼之间形成翼地效应时的压力分布,分析了该情况时水翼的水动力特性以及翼地效应对获能效率的影响。结果表明:合理规划振荡水翼的折算频率、摆角幅值、升沉振幅、转轴位置等参数均可以提高水翼的能量捕获效率；水翼在振荡运动过程中,涡脱落的产生将会影响到水翼的获能效率；平行对称双水翼之间的翼地效应会使双翼之间的流域形成高压区,提高水翼升力；增加的升阻比有利于提高水翼的能量捕获效率,在双翼最小间距缩小时,水翼的获能效率会因地面效应作用的增强而提高。

Abstract:

This paper aims to study the influence of motion parameters on the power-extraction efficiency of oscillating hydrofoils in tidal current, investigate the distributions of the motion parameters of hydrofoils at high power-extraction efficiency, and improve the power-extraction efficiency of oscillating hydrofoils in tidal power-extraction devices. A numerical calculation model of oscillating hydrofoils was established based on the overset grid technique, and the effectiveness of the grid was verified. By modifying the motion parameters of a hydrofoil including reduced frequency f^*, pitching amplitude θ₀, and heave amplitude h₀, the hydrodynamic characteristics of two-dimensional oscillating hydrofoil and the corresponding power-extraction efficiency were investigated. In addition, the influence of vortex shedding on the power-extraction efficiency during the motion of the hydrofoil was analyzed. The pressure distribution when the wing-in-ground effect was formed between two hydrofoils was also studied. The hydrodynamic characteristics of the hydrofoil and the influence of the wing-in-ground effect on the power-extraction efficiency were analyzed under this circumstance. Results show that reasonable planning of the reduced frequency, pitching amplitude, heaving amplitude, and shaft position of the oscillating hydrofoil could all improve the power-extraction efficiency. The generation of vortex shedding during the oscillating motion of the hydrofoil could affect the power-extraction efficiency. The wing-in-ground effect between the parallel symmetrical double hydrofoils would form a high-pressure area in the flow field between the two hydrofoils and increase the lift of the hydrofoils. Increasing the lift-to-drag ratio was beneficial to improve the power-extraction efficiency. When the minimum distance between the two hydrofoils reduced, the power-extraction efficiency of the hydrofoil increased due to the enhancement of ground effect.