A Method for Preliminary Rotor Design – Part 1: Radially Independent Actuator Disk model

Abstract. We present an analytical model for assessing the aerodynamic performance of a wind turbine rotor though a different parametrization of the the classical Blade Element Momentum (BEM) model. The model is named the Radially Independent Actuator Disc model (RIAD) and it establishes an analytical relationship between the local-thrust loading and the local-power, known as the Local-Thrust-Coefficient and the Local-Power-Coefficient respectively. The model has a direct physical interpretation, showing the contribution for each of the 3 losses: wake-rotation-loss, tip-loss and viscous-loss. The gradients for RIAD is found through the use of the Complex-step-method and power optimization is used to show how easily the method can be used for rotor optimization. The main benefit of RIAD is the ease at which it can be applied for rotor optimization, and especially load constraint power optimization as it is described in Loenbaek et al. (2020). The relationship between the RIAD input and the rotor chord and twist is established and it is validate against a BEM solver.