code: def Gr(L: float, Ts: float, Tf: float, beta: float, nu: float, g: float):
      
  
      return g * beta * (Ts - Tf) * L**3.0 / nu**2.0
docs: Calculate the Grashof number.
  
      :param L: [m] heat transfer surface characteristic length.
      :param Ts: [K] heat transfer surface temperature.
      :param Tf: [K] bulk fluid temperature.
      :param beta: [1/K] fluid coefficient of thermal expansion.
      :param nu: [m2/s] fluid kinematic viscosity.
  
      :returns: float
  
      .. math::
          \\mathrm{Gr} = \\frac{g \\beta (Ts - Tinf ) L^3}{\\nu ^2}
  
      Characteristic dimensions:
          * vertical plate: vertical length
          * pipe: diameter
          * bluff body: diameter