Wind Turbine Response to Analytic Inflow Vortex Parameters Variation: Preprint

As larger wind turbines are placed on taller towers, rotors frequently operate in atmospheric conditions that support organized, coherent turbulent structures. It is hypothesized that these structures have a detrimental impact on the blade fatigue life experienced by the wind turbine. These structures are extremely difficult to identify with sophisticated anemometry such as ultra-sonicanemometers. In order to ascertain the idealized worst-case scenario for vortical inflow structures impinging on a wind turbine rotor, we created a simple, analytic vortex model. The Rankine vortex model assumes the vortex core undergoes solid body rotation to avoid a singularity at the vortex center and is surrounded by a 2-dimensional potential flow field. Using the wind turbine as a sensorand the FAST wind turbine dynamics code with limited degrees of freedom, we determined the aerodynamic loads imparted to the wind turbine by the vortex structure. The size, strength, rotational direction, plane of rotation, and location of the vortex were varied over a wide range of operating parameters. We identified the vortex conformation with the most significant effect on blade root bendingmoment cycle amplitude. Vortices with radii on the scale of the rotor diameter or smaller caused blade root bending moment cyclic amplitudes that lead to reduced fatigue life. The rotational orientation, clockwise or counter-clockwise produces little difference in the bending moment response. Vortices in the XZ plane produce bending moment amplitudes significantly greater than vortices in the YZplane. The response to vortices in the inflow is similar for both 2- and 3-blade turbines.