Modeling Dynamic Stall for a Free Vortex Wake Model

Abstract

Floating offshore wind turbines in deep waters offer significant advantages to onshore and near-shore wind turbines. However, due to the motion of floating platforms in response to wind and wave loading, the aerodynamics are substantially more complex. Traditional aerodynamic models and design codes do not adequately account for the floating platform dynamics. Previous research at the University of Massachusetts, Amherst developed the Wake Induced Dynamics Simulator, or WInDS, a free vortex wake model of wind turbines that explicitly includes the velocity components from platform motion. WInDS rigorously accounts for the unsteady interactions between the wind turbine rotor and its wake, however, as a potential flow model, the unsteady viscous response in the blade boundary layer is neglected. This work addressed this concern through the integration of a Leishman-Beddoes dynamic stall model into WInDS. Several improvements to the Leishman-Beddoes dynamic stall model are proposed to improve the synthesis of 2D steady airfoil data and to improve stability when couple with WInDS. The stand-alone dynamic stall model was validated against 2D unsteady data from the OSU pitch oscillation experiments and the coupled WInDS model was validated against three-dimensional data from NREL's UAE Phase VI campaign. WInDS with dynamic stall shows substantial improvements in load predictions under unsteady conditions. WInDS with the dynamic stall model should provide the necessary aerodynamic model fidelity for future research and design work on floating offshore wind turbines.