This information is part of the Modelica Standard Library maintained by the Modelica Association.

Loss factor for mass flow rate from port_a to port_b (Idelchik 1994, diagram 4-14, p. 221):

zeta = [(1-A0/A1) + 0.707*(1-A0/A1)^0.375]^2*(A1/A0)^2
       for Re(A0) ≥ 1e5,  independent of alpha

Loss factor for mass flow rate from port_b to port_a (Idelchik 1994, diagram 4-13, p. 220, with A2=A1):

zeta = k*(1 - A0/A1)^0.75 + (1 - A0/A1)^2 + 2*sqrt(k*(1-A0/A1)^0.375) + (1- A0/A1)
       k  = 0.13 + 0.34*10^(-(3.4*LD+88.4*LD^2.3))
            (there is a typing error in the formula in diagram 4-13, the above
             equation corresponds to table (a) in diagram 4-12)
       LD = L/D0
       for Re(A0) ≥ 1e4, 40 deg ≤ alpha ≤ 60 deg
                          for other values of alpha, k is given as table
                          in diagram 3-7 (this is not yet included in the function)

data = sharpEdgedOrifice(diameter, leastDiameter, length, alpha)

diameter	Type: Diameter (m) Description: Inner diameter of pipe (= same at port_a and port_b)
leastDiameter	Type: Diameter (m) Description: Smallest diameter of orifice
length	Type: Diameter (m) Description: Length of orifice
alpha	Type: Angle_deg (°) Description: Angle of orifice

data	Type: LossFactorData Description: Pressure loss factors for both flow directions