Energy supply is the basis for the development of a modern society. Nowadays most of the energy supply is based on fossil fuels. Nevertheless, the use of renewable energy has increased significantly during the recent years.

Wind energy is one of the important sources of renewable energy.

Horizontal axis wind turbines (HAWT) are by far the most popular means of converting wind energy into electrical energy. The research on HAWT has been focused on the case of axial flow where the direction of the incoming wind is parallel to the turbine axis. Nevertheless, wind changes its direction continuously and thus most of the time wind turbines work in yawed flow where there exists a finite angle between the turbine axis of rotation and wind direction. Yawed results in a reduction in the energy production, but more important is the fact that it results in an unsteady behavior: Periodic aerodynamic loads that result in severe fatigue problems in the various components of the turbine.

The aim of the present research is to develop an efficient method of calculating the aerodynamic loads that act along the wind turbine blades while it operates in yawed flow.

The research consists of two main parts:

In the first part a new actuator disk model for calculating the induced velocities over the disk, is combined with a blade element model for calculating the loads along the blades. The new actuator disk model is capable of modeling the non-uniform characteristics of the flow across the disk (in the radial and circumferential directions) due to the yawed flow. Because of the unsteady aerodynamic characteristics of the blade cross-sectional incoming flow, the blade-element model includes the influence of unsteady effects on the blade cross-sectional aerodynamic coefficients.

in the second model the loads along the blades are calculated again using the blade-element model. The induced velocity in the flow field is calculated after the pressure field is calculated by a solution of the pressure wave equation. The input to the wave equation (Ffowcs, Williams, Hawking equation) are the loads along the blades. Various numerical methods and approximations are used in order to make the calculations more efficient.