docs: def Nu_vertical_cylinder_Griffiths_Davis_Morgan(Pr, Gr, turbulent=None):
      r'''Calculates Nusselt number for natural convection around a vertical
      isothermal cylinder according to the results of [1]_ correlated by [2]_, as
      presented in [3]_ and [4]_.
  
      .. math::
          Nu_H = 0.67 Ra_H^{0.25},\; 10^{7} < Ra < 10^{9}
  
          Nu_H = 0.0782 Ra_H^{0.357}, \; 10^{9} < Ra < 10^{11}
  
      Parameters
      ----------
      Pr : float
          Prandtl number [-]
      Gr : float
          Grashof number [-]
      turbulent : bool or None, optional
          Whether or not to force the correlation to return the turbulent
  		 result; will return the laminar regime if False; leave as None for
          automatic selection
  
      Returns
      -------
      Nu : float
          Nusselt number, [-]
  
      Notes
      -----
      Cylinder of diameter 17.43 cm, length from 4.65 to 263.5 cm. Air as fluid.
      Transition between ranges is not smooth.
      If outside of range, no warning is given.
  
      Examples
      --------
      >>> Nu_vertical_cylinder_Griffiths_Davis_Morgan(.7, 2E10)
      327.6230596100138
  
      References
      ----------
      .. [1] Griffiths, Ezer, A. H. Davis, and Great Britain. The Transmission of
         Heat by Radiation and Convection. London: H. M. Stationery off., 1922.
      .. [2] Morgan, V.T., The Overall Convective Heat Transfer from Smooth
         Circular Cylinders, in Advances in Heat Transfer, eds. T.F. Irvin and
         J.P. Hartnett, V 11, 199-264, 1975.
      .. [3] Popiel, Czeslaw O. "Free Convection Heat Transfer from Vertical
         Slender Cylinders: A Review." Heat Transfer Engineering 29, no. 6
         (June 1, 2008): 521-36. doi:10.1080/01457630801891557.
      .. [4] Boetcher, Sandra K. S. "Natural Convection Heat Transfer From
         Vertical Cylinders." In Natural Convection from Circular Cylinders,
         23-42. Springer, 2014.
      '''
      Ra = Pr*Gr
      if turbulent or (Ra > 1E9 and turbulent is None):
          Nu = 0.0782*Ra**0.357
      else:
          Nu = 0.67*Ra**0.25
      return Nu