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air_density_adjustment

Functions:

  • apply_air_density_adjustment –

    Applies air density corrections to the wind speed values following suggestions by the IEC 61400-12-1:2017 [1].

apply_air_density_adjustment 

apply_air_density_adjustment(
    wind_speed, pressure, temperature, height=0
)

Applies air density corrections to the wind speed values following suggestions by the IEC 61400-12-1:2017 [1].

Parameters:

  • wind_speed

    (float or array - like) –

    The wind speed values in m/s.

  • pressure

    (float or array - like) –

    Air preassure in Pa.

  • temperature

    (float or array - like) –

    Air temperature in degree Celsius.

  • height

    (float or array - like, default: 0 ) –

    The (hub) height of that the air density is going to be adjusted to in m, by default 0

Returns:

  • numeric or array - like –

    The air density corrected wind speed in m/s at the given height.

Notes 
Ideal gas equation applied since it is nearly equivalent to a real-gas equation at humidity = 0, and humidity does not have a significant impact until high temperatures are considered.
Pressure projection using barometric equation and density correction from assuming equal energy in the wind.
References

[1] International Electrotechnical Commission (ICE). (2017). IEC 61400-12-1:2017 (p. 558). https://webstore.iec.ch/publication/26603

Source code in reskit/wind/core/air_density_adjustment.py 
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def apply_air_density_adjustment(wind_speed, pressure, temperature, height=0):
    """
    Applies air density corrections to the wind speed values following suggestions by the IEC 61400-12-1:2017 [1].

    Parameters
    ----------
    wind_speed : float or array-like
        The wind speed values in m/s.
    pressure : float or array-like
        Air preassure in Pa.
    temperature : float or array-like
        Air temperature in degree Celsius.
    height : float or array-like, optional
        The (hub) height of that the air density is going to be adjusted to in m, by default 0

    Returns
    -------
    numeric or array-like
        The air density corrected wind speed in m/s at the given height.

    Notes
    -----
        Ideal gas equation applied since it is nearly equivalent to a real-gas equation at humidity = 0, and humidity does not have a significant impact until high temperatures are considered.
        Pressure projection using barometric equation and density correction from assuming equal energy in the wind.

    References
    ----------
    [1] International Electrotechnical Commission (ICE). (2017). IEC 61400-12-1:2017 (p. 558). https://webstore.iec.ch/publication/26603

    """
    g0 = 9.80665  # Gravitational acceleration [m/s2]
    Ma = 0.0289644  # Molar mass of dry air [kg/mol]
    R = 8.3144598  # Universal gas constant [N·m/(mol·K)]
    rhoSTD = 1.225  # Standard air density [kg/m3]

    temperature = temperature + 273.15

    # Get surface density
    rho = pressure * Ma / (R * temperature)

    # Project rho to the desired height
    if not height is None:
        rho = rho * np.exp((-g0 * Ma * height) / (R * temperature))

    # Adjust wind speeds to standard-air-density-equivalent
    return np.power(rho / rhoSTD, 1 / 3) * wind_speed