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Aungier's Modified Redlich-Kwong Real Gas Equation Of State

Many of the CompAero TurbAero aerodynamic design and analysis programs feature a very general equation of state for ideal and non-ideal fluids and fluid mixtures developed by Ron Aungier. This model is a modified form of the popular two-parameter Redlich-Kwong equation of state extended to include the effects of accentric factor and critical-point compressibility factor. It also employs generalized models for two-phase (liquid-vapor) fluids to handle condensing fluids in turbines.


The gas property data required for this equation are:

  1. Molecular weight

  2. Critical temperature

  3. Critical pressure

  4. Crirtical compressibility factor

  5. Accentric factor

  6. A polynomial expression for low-pressure specific heat (Cp) as a function of temperature


All of these gas property data are readily available for most compounds of interest from several standard publications (e.g., Yaws, C. L., Chemical Properties Handbook, McGraw-Hill, 1999). Both CompAero and TurbAero offer this equation of state in two stand-alone programs for user convenience as well as in the various design & analysis programs.


  • Program RKMOD: an ideal/non-ideal fluid equation-of-state package for a variety of thermodynamic property calculations.

  • Program GASDATA: a gas property database maintenance program to support Program RKMOD and the other programs that use its equation of state (including a current database of over 100 compounds).


This equation of state is described in:


(Aungier, R. H.) "A Fast, Accurate Real Gas Equation Of State for Fluid Dynamic Analysis Applications", Transactions of the ASME, Journal of Fluids Engineering, June 1995, pp. 277-281. Also in Contributed Papers In Fluids Engineering 1994, ASME FED-Vol. 182, 1994, pp. 1-6

(the original reference).


(Aungier, R. H.) Turbine Aerodynamics: Axial-Flow and Radial-Inflow Turbine Design and Analysis, ASME Press, 2006

(this reference includes the most complete description of the general two-phase flow models).


(Aungier, R. H.) Axial-Flow Compressors: A Strategy for Aerodynamic Design and Analysis, ASME Press, 2003.


(Aungier, R. H.) Centrifugal Compressors: A Strategy for Aerodynamic Design and Analysis, ASME Press, 2000.


(Aungier, R. H.) "Thermodynamic State Relations," The Handbook Of Fluid Dynamics (Johnson, R. W., editor), by CRC Press LLC, 1998

pp. 4-29 to 4-34.

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