Numerical simulation on aerodynamic performance enhancement of J-shaped vertical-axis wind turbines using gurney flaps

Vertical-axis wind turbines (VAWTs) often suffer from poor self-starting behavior and limited torque generation, especially under low-wind conditions. While passive flow-control devices have been explored to improve these limitations, the aerodynamic effects of Gurney flaps (GFs) on J-shaped blades remain insufficiently understood. In this study, two-dimensional unsteady Reynolds-averaged Navier–Stokes (RANS) simulations with the k-ω; Shear-Stress Transport (SST) turbulence model were conducted to systematically investigate the aerodynamic performance of three GF configurations—outboard, inboard, and two-sided—over a wide range of tip-speed ratios. Rather than simply re-identifying a previously reported optimum case, this work focuses on a broader comparison of GF position and height effects and provides a detailed azimuth-resolved analysis of the aerodynamic mechanisms responsible for the performance differences. The results show that, under the present two-dimensional numerical conditions, the 0.75% chord inboard GF provides the most favorable aerodynamic performance at moderate TSRs by enhancing circulation and pressure loading in the upwind power-producing sector. Two-sided GFs offer moderate benefits by stabilizing blade loading, while outboard GFs may improve torque relative to the clean rotor at some TSRs but remain less effective than the inboard configuration because of stronger separation, wake unsteadiness, and torque fluctuations. These numerical findings suggest that small inboard Gurney flaps may be a promising passive flow-control option for J-shaped Darrieus VAWTs under the simplified conditions considered in this study; however, further three-dimensional simulations and experimental validation are required before their practical engineering performance under realistic operating environments can be confirmed.