基于单/双向流固耦合的水翼水力阻尼数值预测方法研究

为评估水力机械外部瞬态载荷作用下的动力响应幅值，必须考虑流固耦合产生的水力阻尼效应。如何准确预测水下结构水力阻尼参数是设计阶段评价水力机械运行稳定性的难点问题。借助分离式单/双向流固耦合数值模拟方法，针对工程中常用的NACA0009翼型，开展了水翼在5~20 m/s流速下的振动特性和水力阻尼比数值预测方法研究。分析结果表明：第1阶弯曲模态振型在静水中与20 m/s流速下相一致，且低阶模态水翼固有频率随流速变化在3.95%以内，据此，单向流固耦合中将静水中振型及固有频率作为动水水翼的初始条件的假设是可行的。基于单向流固耦合方法所预测的水力阻尼比与实验值的平均相对偏差为11.42%。双向流固耦合则不需要该假设，能更加准确地预测低阶模态固有频率、水翼尾部脱落涡频率和水力阻尼比，相对实验值的平均偏差分别为4.36%、4.24%和4.95%。单/双向流固耦合数值方法都能预测水力阻尼比随流速线性增加的规律。本文算例中，相同计算资源条件下双向流固耦合所需计算时间是单向计算的15倍。在实际工程应用中，推荐优先采用单向流固耦合方法。

Research on numerical prediction methods of hydrodynamic damping ratio for a hydrofoil based on one-way and two-way fluid-structure interactions

In order to evaluate the dynamic response amplitude of a hydraulic machinery induced by external transient load, the hydrodynamic damping effect caused by fluid-structure interaction (FSI) must be considered. How to accurately predict the hydrodynamic damping parameters of an underwater structure is a difficult problem in evaluating the stability of hydraulic machinery during the design stage. The studies on the vibration characteristics and hydrodynamic damping ratio predicting methods of a NACA 0009 hydrofoil are carried out by one-way and two-way FSI numerical simulations, at the velocities range from 5-20m/s. The simulation results show that:the first bending mode shapes are consistent in still water and at the velocity of 20m/s, and the relative variations of natural frequencies for low-order modes of hydrofoil are within 3.95% under different velocities. Based on this, proved that the assumption of mode shape and natural frequency independent on the velocity for one-way FSI method is reasonable. The averaged relative deviation between hydrodynamic damping obtained by one-way FSI and experiment is 11.42%. Two-way FSI does not require this assumption, which offers higher accuracy to predict the natural frequencies of low-order modes, the vortex shedding frequencies of the hydrofoil and the hydrodynamic damping ratios, with averaged relative deviations of 4.36%, 4.24% and 4.95%, respectively, compared with the experimental results. Both one-way and two-way FSI methods can obtain the relationship that the hydrodynamic damping ratio increases liner with velocity. While in the example in this paper, the calculation time required for the two-way FSI is 15 times of the one-way FSI under the same computing resource conditions. In practical engineering applications, it is recommended to use the one-way FSI method in order to save time.