Aerodynamic Model of Horizontal Axis Wind Turbines in Yawed Flow

An aerodynamic model for the analysis of horizontal axis wind turbines in yawed flow is presented. The model is based on a solution of the wave equation to find the induced velocities due to the rotating blades. Previously this model was applied successfully to analyze a wind turbine in an axial flow. This paper presents the capability of the model to analyze a turbine working under yawed, unsteady flow conditions. The aerodynamic loads along the blades are calculated using a blade-element model, where the velocities "seen" by the blades cross sections are obtained from the solution of the wave equation. The problem is nonlinear and thus is solved by an iterative procedure. Various approximations and analytical derivations are used to increase the efficiency of the calculations. The results of the model are compared with wind tunnel test results. The comparisons include the loads along the blades and the induced velocities. Good agreement is shown between the calculated and measured variables.