Performance analysis of vertical-axis wind turbine clusters: Effect of inter-turbine spacing and turbine rotation

Wind energy has emerged as a viable alternative to fossil fuels, with vertical-axis wind turbines (VAWTs) gaining popularity due to their efficiency and adaptability. Combining the actuator line method (ALM) with large eddy simulation (LES) enables accurate performance evaluations, facilitating the design and optimization of wind turbines. The present study invokes ALM-based methodology to perform calculations for the VAWTs. The results of the LES simulations of the VAWTs have been extensively validated against the available experimental and numerical data. The study further explores a VAWT cluster of three turbines by investigating the influence of turbine spacing (in both inline and staggered configuration) on cluster performance. This study shows that the configuration with a streamwise separation (X-sep) of 0.34 D and a transverse separation (Y-sep) of 2.5 D exhibits superior performance to other combinations owing to increased kinetic energy in the wake for the downstream turbines. Furthermore, we have presented the effect of varying the rotation direction (in combinations of Clockwise and Counterclockwise rotation) for the individual turbines in the 3-turbine cluster for the two configurations: inline (X-sep = 0 D, Y-sep = 2.5 D) and staggered (X-sep = 0.34 D, Y-sep = 2.5 D). Staggered counter-rotating turbine cases show reduced performance compared to co-rotating cases, specifically, the clockwise co-rotating (C-C-C) configuration. In the inline configuration, counter-rotating setups outperform co-rotating ones. Counter-rotation analysis reveals that reducing streamwise separation allows turbines to align in line without sacrificing performance, thereby increasing the power density of the turbine cluster.