def Yen(Re):
    """Calculates drag coefficient of a smooth sphere using the method in
    [1]_ as described in [2]_.

    .. math::
        C_D = \\frac{24}{Re}\\left(1 + 0.15\\sqrt{Re} + 0.017Re\\right)
        - \\frac{0.208}{1+10^4Re^{-0.5}}

    Parameters
    ----------
    Re : float
        Reynolds number of the sphere, [-]

    Returns
    -------
    Cd : float
        Drag coefficient [-]

    Notes
    -----
    Range is Re <= 2E5

    Examples
    --------
    >>> Yen(200.)
    0.7822647002187014

    References
    ----------
    .. [1] B.C. Yen, Sediment Fall Velocity in Oscillating Flow, University of
       Virginia, Department of Civil Engineering, 1992.
    .. [2] Barati, Reza, Seyed Ali Akbar Salehi Neyshabouri, and Goodarz
       Ahmadi. "Development of Empirical Models with High Accuracy for
       Estimation of Drag Coefficient of Flow around a Smooth Sphere: An
       Evolutionary Approach." Powder Technology 257 (May 2014): 11-19.
       doi:10.1016/j.powtec.2014.02.045.
    """
    Cd = 24.0 / Re * (1 + 0.15 * Re ** 0.5 + 0.017 * Re) - 0.208 / (1 + 
        10000.0 * Re ** -0.5)
    return Cd
