Stodola method applies an "ellipse law" to the behavior of a multistage turbine. It is often used in steam turbine practice but can also be used in single phase, however, this approach is most suited for high pressure ratios.
Equation 4.32 of Source 1 or http://www.thermopedia.com/content/1222/
m_flow*sqrt(T_inlet)/p_inlet = k*sqrt(1-(p_outlet/p_inlet)^2)
Note: k has been multiplied by the constant sqrt(R) where R is gas constant.
Source
1. S. L. DIXON, Fluid mechanics and thermodynamics of turbomachinery, 4. ed. in SI/metric units, Butterworth-Heinemann, Boston, Mass. (1998).