Unraveling extreme tornado–turbine interactions: A modal perspective for interpreting extreme loads and flow structures

Abstract

Wind turbines are increasingly exposed to tornadoes, yet the aerodynamic loading mechanisms and flow physics governing tornado–turbine interactions remain poorly understood. In this study, a numerical wind tunnel based on large-eddy simulations is developed and validated to reproduce both atmospheric boundary layer (ABL) and tornado flows. The National Renewable Energy Laboratory 5-MW wind turbine is employed as a representative model, and proper orthogonal decomposition is used to identify the dominant coherent structures and their associated flow dynamics. The results show that tornado-induced loads far exceed those under ABL, with distributions strongly influenced by swirl ratio, blade spatial position, chord length, and twist distribution. Windward blade orientation significantly affects pressure distributions and dominant modes, while leading and trailing edges experience strong fluctuations. Flow separation and vortex formation are strongly influenced by surface orientation, spanwise location, and swirl ratio. Notably, the first three pressure modes and two velocity modes capture over 90% of the total modal energy, enabling reconstruction of turbine–tornado interactions with only a few dominant coherent structures. Furthermore, comparisons with the translating tornado cases examined in our previous study show that the stationary tornado simulation provides reasonable estimates of the principal blade loading characteristics under the investigated conditions.