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Table of Contents

Modelling the Wind

The wind field incident on the turbine may be specified in a number of ways. For some simple calculations, a uniform, constant wind speed is assumed, such that the same incident wind speed is seen by every point on the rotor. For more detailed calculations however, it is important to be able to define both the spatial and temporal variations in wind speed and direction.

The steady-state spatial characteristics of the wind field may include any combination of the following options:

  • Wind shear: the variation of wind speed with height.
  • Tower shadow: distortion of the wind flow by the wind turbine tower.
  • Upwind turbine wake: full or partial immersion of the turbine rotor in the wake of another turbine operating further upwind.

The wind direction must also be specified, both relative to the direction in which the nacelle is pointing (to define the yaw error), and relative to the horizontal plane (to define the upflow angle). The latter effect may be important for turbines operating in hilly terrain.

For simulations, it is also important to be able to define how the wind speed and direction vary with time. The following models are provided:

  • Constant wind: no variation with time.
  • Single point history: a time history of wind speed and direction, which is fully coherent over the whole rotor, is specified as a lookup table against time. Linear interpolation is used between the time points.
  • 3D turbulent wind: this option uses a pre-generated 3-dimensional turbulent wind field with defined spectral and spatial coherence characteristics representative of real atmospheric turbulence.
  • IEC transients: this option uses wind speed and direction transients as defined by the IEC 61400-1 standard. It is intended for evaluating specific load cases, for example during extreme gusts.

Wind reference height

The mean wind speed is defined at a specified height referred to as a reference height. In steady flow conditions the wind speed at other heights will be modified according to the wind shear selected. The user can specify either a reference height or the hub height of the turbine.

Wind modelling behaviours

If the wind field is queried below the ground or mean water level (MWL) then it is assumed that the height is zero. The height will influence the calculation of the wind speed via the wind shear factor between the hub height and the point at which the wind speed is being evaluated. But it does not effect any of the following contributions to the wind velocity:

  • Transient changes in wind speed or direction: in this scenario the “amplitude of change” will be unmodified by proximity to the ground whereas the starting values are influenced by the height as per the above explanation;

  • Turbulent fluctuations read from a .wnd file and added to the mean wind speed are unmodified with respect to the height during time domain simulation.

User-Defined Wind Model

If the user would like to include a wind model that is not available using existing options in Bladed then they can use the Wind DLL modelling option. This allows the user to write some code that describes the wind conditions and co-simulate with Bladed during a dynamic simulation.

Last updated 10-09-2024