Aeroelastic analysis of the 3-dimensional interference patterns of wind-turbine rotors: The 3-D DRD-BEM model

Greater penetration of wind energy demands better utilization of available wind. This has led to a formidable increase in the size of turbine rotors over the past few years. Bigger rotors call for lighter, more flexible blades to reduce loads and improve fatigue life. As a result, future blades will deform substantially more than the relatively stiff blades of the past. More efficient use of wind power also calls for incorporating advanced active and passive control strategies and increasing the range of velocities over which wind energy is captured. The blade sections will, therefore, no longer be perpendicular to the rotor's radial direction. The hitherto small radial component of aerodynamic forces in the hub must now be taken into account. In this paper we present a way to substantially extend the capabilities of the Dynamic Rotor Deformation - Blade Element Momentum model (DRD-BEM) by taking into consideration the 3-Dimensional effects of these forces on rotor interference. In this method, called the 3-D DRD-BEM, the coordinate system where the momentum balance is performed in BEM theory is moved, from the hub, to the instantaneous position and alignment of the blade section in its deformed configuration. A detailed description of the new model is presented, followed by numerical simulations to verify it in a 3-D interference pattern.