Effects of helical-shaped blades on wake characteristics and power production of vertical-axis wind turbines in finite-length wind farms*

Recent experimental and numerical studies based on single-turbine tests have suggested that using helical-shaped blades on vertical-axis wind turbines (VAWTs) may induce beneficial effects to the wake flow characteristics, such as faster wind speed recovery and lower turbulent intensity. In this work, the large-eddy simulation (LES) method is utilized to further test the effects of helical-shaped blades on VAWTs in wind farm environments. In particular, two helical-bladed VAWTs (with opposite blade twist angles) and one straight-bladed VAWT are considered. Each VAWT type is tested in three different aligned finite-length array configurations with coarse, intermediate and tight turbine spacings. Statistical analyses of the flow field and VAWT performance are conducted based on the LES data of these nine simulation cases. The results indicate that using the helical-bladed VAWTs may help increase the power production rate in the fully developed flow region of the VAWTs array by about 3-7%. Compared with the straight-bladed VAWT, the helical-bladed VAWTs have smoother coverage of the azimuth rotation angle during the rotation, resulting in significant reductions of temporal fluctuations in power coefficient and structural bending moment.