Characterization of vortex shedding regimes and lock-in response of a wind turbine airfoil with two high-fidelity simulation approaches

Abstract. In this work, the Vortex-Induced Vibrations (VIV) phenomenon affecting a wind turbine airfoil section is analysed with two numerical approaches, a two-dimensional (2D) setup of the airfoil, simulated using the Unsteady Reynolds-averaged Navier–Stokes equations, and a three-dimensional (3D) setup with a span-to-chord aspect ratio of 1, employing the Delayed Detached Eddy Simulation model. A constant inflow velocity normal to the airfoil chord is considered, for a Reynolds number around 2 × 10⁶. The only structural degree of freedom is the airfoil chordwise displacement. As a reference, simulations of the static airfoil are also performed. The 3D static simulation lift coefficient is shown to have intermittent periods of very different characteristics, including different Strouhal numbers. The VIV simulations are performed at different inflow velocities to cover the lock-in range. To make the lock-in range non-dimensional, a single Strouhal number is chosen for the 3D case, such that the non-dimensional lock-in ranges predicted by both approaches coincide. This Strouhal number is 5 % higher than the 2D Strouhal number and 14 % lower than the one previously reported for the same 3D airfoil setup. Inside the lock-in range, the 2D and 3D approaches predict a similar VIV development, characterized by the lift coefficient standard deviation, the mean drag coefficient and the airfoil vibration amplitude growth rate. These results are supported by the common hypothesis that the three-dimensional vortex shedding coherence increases when the body undergoes large and growing motions, becoming similar to a 2D case.