基于声固耦合法的水翼结构模态特性研究

Modal Characteristics of Hydrofoil Structure Based on Acoustic Fluid-structure Interaction Method

摘要:

模态特性分析是进行水力机械设计的关键环节，当水力激励特性与结构的固有模态契合时，可能导致强烈共振，威胁电站的安全稳定运行。以叶轮的简化模型——水翼为研究对象，采用声固耦合法分析了水翼的干湿模态特性，探究了不同攻角和尾部修型下水翼的模态特性。研究发现，附加质量作用下水翼固有频率大幅度降低，湿模态振型也发生显著变化。攻角线性变化时，水翼固有频率呈现非线性变化趋势，2°攻角下频率最大。攻角增大到10°和15°，水翼固有频率会明显下降，15°时频率最小。攻角变化对水翼前4阶模态的展向模态位移和扭转模态的弦向模态位移影响较小，弯曲模态fs1和fs3的弦向模态位移差异性会增大。尾缘修型情况下，水翼固有频率会增加，30°修型对应的频率最大。尾缘修型对水翼尾缘的变形作用明显，抑制fs1和fs3的弯曲变形，模态位移变化范围明显减小。而且扭转模态fs2、fs4尾缘的弦向模态位移和fs3展向模态位移出现小幅度减小。

Abstract:

Modal characteristic analysis is a crucial step in the design of hydraulic machinery. When the hydraulic excitation characteristics match the natural modes of the structure, it may lead to intense resonance phenomena, threatening the safe and stable operation of the power station. The hydrofoil, a simplified model of the impeller, was taken as the research object. The acoustic fluid-structure interaction method was adopted to analyze the dry and wet modal characteristics of the hydrofoil, and the effects of the angle of attack and trailing edge modifications on the modal characteristics were investigated. It was found that the natural frequency of the hydrofoil was decreased significantly under the effect of the added mass, and the mode shape of the wet mode also changed obviously. When the angle of attack changed linearly, the natural frequency of the hydrofoil showed a non-linear variation trend, with the maximum frequency occurring at an angle of attack of 2°. When the angle of attack increased to 10° and 15°, the natural frequency of the hydrofoil decreased significantly, and the frequency was the smallest at 15°. The change in the angle of attack had little effect on the spanwise modal displacement of the first four-order modes and the chordwise modal displacement of the torsional modes of the hydrofoil, while the difference in the chordwise modal displacement of the bending modes fs1 and fs3 was increased. In the case of trailing edge modification, the natural frequency of the hydrofoil was increased, with the maximum frequency corresponding to the 30° modification. The trailing edge modification had an obvious effect on the deformation of the hydrofoil’s trailing edge: suppressing the bending deformation of fs1 and fs3, and significantly reducing the range of modal displacement changes. Moreover, there was a slight decrease in the chordwise modal displacement values of the tail edges of torsional modes fs2 and fs4, as well as the spanwise modal displacement values of fs3.