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Vortices play a critical role in the operation of VAWTs (Vertical-Axis Wind Turbines). In spite of this, most studies have approached these matters via the qualitative analysis of vortex shedding, and torque-extraction data. These approaches rely only on the visual observation of vortices that can lead to subjective interpretations. In our work, a 3D framework is employed to address this issue. On this basis, the present study establishes a relationship between vorticity, dynamic stall and turbine performance, by examining various locations along the span and the chord of the airfoil. To conduct this analysis, a 3D-CFD (Computational Fluid Dynamics) simulation of an H-Darrieus with a symmetrical NACA 0018, powered by 8 m/s winds, is considered. The CFD simulations are validated based on the agreement of calculated power coefficients, with those obtained from experimental data, reported in the technical literature, with deviations being lower than 4%. The simulation results for various TSRs (Tip Speed Ratios) report new findings concerning the critical stages of VAWT operation. This shows that there is a link between the maximum vorticity, the imminent vortex-separation condition and the dynamic stall, with this being a function of the various axial positions in the VAWT.
Romero et al. (Thu,) studied this question.