windkit.wind.rotor_equivalent_wind_speed

windkit.wind.rotor_equivalent_wind_speed(wind_speed, wind_direction, hub_height, rotor_diameter, delta_z=1.0, n_integrate=1001)[source]

Calculate the rotor equivalent wind speed (REWS) from given wind speed and directions on height levels.

The procedure is as follows:

  1. Find the area of each segment of the rotor spanned area.

  2. Calculate the wind speed at the center of each segment by linearly interpolating the wind speed to the height of the segment center in log-height.

  3. Calculate the wind direction at the center of each segment by linearly interpolating the wind direction to the height of the segment center. Circularity is taken into account here.

  4. Calculate the wind direction at hub height by linearly interpolating the wind direction to the hub height.

  5. Calculate the REWS as the cube root of the sum of the wind speed at each segment center multiplied by the area-weight (area/total) of the segment and the cosine of the difference between the wind direction at the segment center and the wind direction at hub height.

Parameters:

  • wind_speed (xarray.DataArray) – Wind speed on height levels.

  • wind_direction (xarray.DataArray) – Wind direction on height levels.

  • hub_height (float) – Turbine Hub height.

  • rotor_diameter (float) – Turbine rotor diameter.

  • delta_z (float, optional) – Height difference between segments of turbine spanned rotor area (default: 1.0).

  • n_integrate (int, optional) – Number of points to use for integration (default: 1001) of the area of each segment.

Returns:

rews – Rotor equivalent wind speed.

Return type:

xarray.DataArray