This paper presents a parametric study of Vertical-Axis Turbines (VAT) equipped with chordwise-flexible blades. The objective of this study is to assess the possibility of increasing the efficiency of VATs by allowing passive foil deformations that take advantage of the periodically changing hydrodynamic conditions inherent to VATs. The study is carried out with numerical simulations based on a partitioned Fluid–Structure Interaction (FSI) code implemented within OpenFOAM. Two-dimensional URANS numerical simulations are carried out at a Reynolds number of $10^7$ based on the turbine diameter, which is representative of hydrokinetic applications. A single-blade rotor equipped with a chordwise-flexible NACA 0015 profile is considered. The flexibility is located in the rear part of the foil, between the attach point and the trailing edge. The tip-speed ratio range extends from 2 to 8 and the solidity is set to 0.286. The characteristics of the blade are specified with a dimensionless flexibility parameter and a so-called pressure-to-inertia ratio. The pressure-to-inertia values investigated are larger than one and are representative of hydrokinetic applications in water. The flexibility is varied from zero (rigid blade) to large values involving large deformations. The FSI effects related to these two parameters are investigated and the mechanisms that allow efficiency improvements are presented. It is shown that flexibility introduces a stall mitigation mechanism that helps in improving the efficiency of low tip-speed ratio configurations. Flexibility also reduces blades’ drag in the downstream portion of the cycle when the turbine operates at high tip-speed ratios. More specifically, relative efficiency improvement of about 12% to 15% are observed with moderate flexibilities at tip-speed ratios of 2 (lower than optimal) and 6 (higher than optimal). However, at the optimal tip-speed ratio, flexibility strictly reduces the efficiency, although this reduction remains small for moderate flexibilities. Overall, results also show that blade flexibility tends to extend the tip-speed ratio range of high-efficiency configurations, which may provide interesting advantages when the turbine operates in changing flow conditions.

本文介绍了装备有弦向可弯曲叶片的垂直轴涡轮机（VAT）的参数研究。这项研究的目的是通过允许被动箔片变形来利用增值税固有的周期性变化的水动力条件来评估提高增值税效率的可能性。这项研究是基于在OpenFOAM中实施的分区的流固耦合（FSI）代码进行数值模拟而进行的。二维URANS数值模拟是在雷诺数为$\mathrm{1个}{0}^7$基于涡轮直径，这是水动力应用的代表。考虑配备了弦向柔性NACA 0015型材的单叶片转子。柔韧性位于箔的后部，在附着点和后缘之间。尖端速比范围从2扩展到8，并且将坚固性设置为0.286。叶片的特性通过无量纲的挠性参数和所谓的压力惯量比来指定。研究的压力-惯性值大于1，代表了水中的流体动力学应用。灵活性从零（刚性刀片）到涉及大变形的大值不等。研究了与这两个参数相关的FSI效果，并提出了可提高效率的机制。结果显示，灵活性引入了失速缓解机制，有助于提高低叶尖速比配置的效率。当涡轮机以高叶尖速比运行时，灵活性还减少了叶片在循环下游部分的阻力。更具体地说，在2（低于最佳值）和6（高于最佳值）的叶尖速度比下，具有中等柔韧性时，观察到相对效率提高了约12％至15％。但是，在最佳的叶尖速比下，柔韧性会严格降低效率，尽管对于中等柔韧性而言，这种降低仍然很小。总体而言，结果还表明，叶片的柔韧性倾向于扩大高效配置的叶尖速比范围，当涡轮机在变化的流量条件下运行时，这可能会提供有趣的优势。