Horizontal Axis Wind Turbine

Wind Turbine enables the user to model a Horisantal Axis Wind Turbine (HAWT) considering wind load acting on the rigid blades and control system for blade pitch and electrical power extraction.

In order to model a wind turbine a minimum of two bodies is required; one body to represent the blades,hub and the slow-speed shaft (the present rotor body) and one body to represent the support structure for the rotor.
For application of the electrical torque moment a moment coupling between the bodies has to be included.

It is assumed that the origin of the body fixed rotor coordinate system coincides with the hub centre with X-axis aligned in the direction with the rotor (slow speed) shaft i.e from the hub towards the support.
The wind loads on the blades are computed based on the load coefficient description in the air foil library file and together with a blade element momentum (BEM) method.
The applied BEM code includes dynamic inflow, i.e. a time delay on changes of induced velocity related to the time it takes to convect vorticity in the wake downstream, away from the rotor.
With dynamic inflow, the BEM method will give correct time series of rotor and blade loads under conditions of changing blade pitch angle, wind speed and direction, and tower motion.
The main features of the BEM theory are:

  • Induced velocity is calculated assuming momentum balance for a ring-shaped control volume.

  • Blade sections are treated as independent.

  • Aerodynamic coefficients from wind tunnel tests are used for the blades.

  • Empirical corrections are used for tip-vortices and cascade effects / lift amplification.

The BEM theory is a proven, simple and CPU efficient method to simulate rotor aerodynamics and the method represents the industry standard.

Requirements to wind turbine modeling

  • Support body and rotor (present) body with 6 degrees of freedom

  • Moment coupling attached to the rotor body in direction parallel with body fixed X-axis, ie. Moment around the X axis

Recommendations to wind turbine modeling

The rotor body and the support body may connected by use of

  • 2 docking cone couplings to transfer radial forces. Each docking cone coupling has its contact point located in the rotor body X-axis and its cone attached to the support body. A distance between the two contact points on the rotor axis is necessary in order to transfer moments about y- and z-axes. The orientation of the direction vector of the docking cones should be coincident with the rotor body X-axis.

  • 1 axial force coupling between the rotor body and the support body to transfer axial rotor force. The axial force coupling should be aligned with the rotor body X-axis.

Note that the applied electical torque is handled by Moment Coupling. Thus, no constant moment should be specified for the coupling.
Any specified torsional stiffness will be set to zero during dynamic analysis.