A CFD Model for Real Gas Effects in Turbomachinery

In the design of industrial turbines and compressors, different evolving fluids are encountered, working over a wide range of thermodynamic operating conditions. In most cases, the perfect gas model is accurate enough to describe the physical characteristics of the fluid. However, there is a number of applications for which such an approach is not satisfactory. In steam turbine LP stages, thermodynamic transformations occur near or above the saturation curve of steam, where a bi-phasic fluid is present. Also some centrifugal cryogenic compressors make use of complex mixtures of gases, whose behavior at operating conditions is far from ideal. As far as gas turbines are concerned, the behavior of the combustion products deviates from that of a perfect gas basically from a caloric point of view, and is well represented by the ideal gas equation of state so that the gas model should only account for the variation of specific heat with temperature. A numerical model to account for real gas effects was included in the TRAF code (Arnone [1]), a three-dimensional viscous steady and unsteady RANS solver. In this model the behavior of real gases, gas mixtures or steam is reproduced by replacing analytic relationships of the perfect gas with the use of gas property tables.