There could be several potential ways of getting an average wind speed over the rotor swept area. Which method is actually used in Bladed?
Rotor average longitudinal wind speed is calculated by the following algorithm :
- Divide each blade into sections where each section is bounded by a blade station at each end. If there are N stations, then there will be N-1 sections.
- Divide rotor disc into annular "strips" swept out by these sections.
- Use normal wind model to determine instantaneous longitudinal wind speed at each blade station (taking into account such factors as wind shear, turbulence, upwind turbine wake etc as per user settings).
- Get the average wind speed for each section of each blade by averaging the two station speeds at the ends of this section.
- Assign each blade section speed a weighting factor corresponding to one-third of the area of the corresponding annular strip (assuming three blades).
- Calculate the weighted sum of all the blade section speeds.
- Divide the result by the rotor swept area to get an overall average.