def helical_turbulent_fd_Mori_Nakayama(Re, Di, Dc):
    """Calculates Darcy friction factor for a fluid flowing inside a curved 
    pipe such as a helical coil under turbulent conditions, using the method of 
    Mori and Nakayama [1]_, also shown in [2]_ and [3]_.
        
    .. math::
        f_{curv} = 0.3\\left(\\frac{D_i}{D_c}\\right)^{0.5}
        \\left[Re\\left(\\frac{D_i}{D_c}\\right)^2\\right]^{-0.2}\\left[1 
        + 0.112\\left[Re\\left(\\frac{D_i}{D_c}\\right)^2\\right]^{-0.2}\\right]

    Parameters
    ----------
    Re : float
        Reynolds number with `D=Di`, [-]
    Di : float
        Inner diameter of the coil, [m]
    Dc : float
        Diameter of the helix/coil measured from the center of the tube on one
        side to the center of the tube on the other side, [m]

    Returns
    -------
    fd : float
        Darcy friction factor for a curved pipe [-]

    Notes
    -----    
    Valid from the transition to turbulent flow up to 
    :math:`Re=6.5\\times 10^{5}\\sqrt{D_i/D_c}`. Does not use a straight pipe 
    correlation, and so will not converge on the
    straight pipe result at very low curvature.

    Examples
    --------
    >>> helical_turbulent_fd_Mori_Nakayama(1E4, 0.01, .2)
    0.037311802071379796

    References
    ----------
    .. [1] Mori, Yasuo, and Wataru Nakayama. "Study of Forced Convective Heat 
       Transfer in Curved Pipes (2nd Report, Turbulent Region)." International 
       Journal of Heat and Mass Transfer 10, no. 1 (January 1, 1967): 37-59.
       doi:10.1016/0017-9310(67)90182-2. 
    .. [2] El-Genk, Mohamed S., and Timothy M. Schriener. "A Review and 
       Correlations for Convection Heat Transfer and Pressure Losses in 
       Toroidal and Helically Coiled Tubes." Heat Transfer Engineering 0, no. 0
       (June 7, 2016): 1-28. doi:10.1080/01457632.2016.1194693.
    .. [3] Ali, Shaukat. "Pressure Drop Correlations for Flow through Regular
       Helical Coil Tubes." Fluid Dynamics Research 28, no. 4 (April 2001): 
       295-310. doi:10.1016/S0169-5983(00)00034-4.
    """
    term = (Re * (Di / Dc) ** 2) ** -0.2
    return 0.3 * (Dc / Di) ** -0.5 * term * (1.0 + 0.112 * term)
