The oscillating flow is a problem occurring in the stay vane passage of hydro turbines. The improper shape of the stay vane causes wake formation and sheds large eddies in the trailing edge of the stay vane. The wake at the trailing edge of the stay vane produces pressure fluctuation in the stay vane passage, which leads to noise and vibration during the turbine operation. Therefore, the improper shape of the stay vane may cause flow oscillation in the stay vane passage. Thus, a proper shape design of the stay vane considering the oscillating flow is necessary to mitigate the flow instability. Consequently, experiment and CFD analyses showed that the initial stay vane (ISV) shape causes recirculation and pressure fluctuation. An optimum design methodology is adopted to improve the flow behavior around the stay vane. Optimization of the stay vane is also conducted by using two objective functions (turbine efficiency and flow uniformity) and 12 design variables. The optimal stay vane (OSV) shape is attained by a multi-objective genetic algorithm. Finally, the flow behavior in the stay vane passage with ISV and OSV is compared by experiment and CFD analyses. Thus, the flow instabilities are mitigated with OSV. The installation of OSV improved the flow angle distribution, secondary flow, and pressure fluctuation in the Francis hydro turbine.

振荡流是在水轮机的叶片叶片通道中出现的问题。拉杆叶片的形状不当会导致尾流形成，并在拉杆叶片的后缘掉下大涡。静叶后缘的尾流会在静叶通道中产生压力波动，从而在涡轮机运行期间导致噪音和振动。因此，拉杆叶片的不适当形状会在拉杆叶片通道中引起流动振荡。因此，为了减轻流动的不稳定性，需要考虑振荡流动的支撑叶片的适当形状设计。因此，实验和CFD分析表明，初始停留叶片（ISV）形状会导致再循环和压力波动。采用最佳设计方法来改善导流叶片周围的流动性能。还通过使用两个目标函数（涡轮效率和流动均匀性）和12个设计变量来优化拉杆叶片。最佳导叶（OSV）形状由多目标遗传算法实现。最后，通过实验和CFD分析比较了带有ISV和OSV的斜叶通道中的流动行为。因此，使用OSV可以减轻流量不稳定性。OSV的安装改善了弗朗西斯水轮机的流量角分布，二次流量和压力波动。