Many gases, including carbon dioxide and argon, have been considered as alternatives to air as working fluids in a number of design studies for closed and semi-closed gas turbine engines. In many of these studies, it has been assumed that if the gas constant R and specific heat ratio (isentropic exponent) γ are included in the speed and flow parameters, the compressor map or turbine characteristic is applicable to other working fluids. However, similarity arguments show that the isentropic exponent itself is a criterion of similarity and that the turbomachinery characteristics, even when appropriately non-dimensionalized, will in principle vary as the γ of the working fluid varies. This paper examines the effect of γ on turbomachinery characteristics, mainly in terms of compressors. The performance of a centrifugal compressor stage was measured using air (γ = 1.4), CO2 (γ = 1.29), and argon (γ = 1.67). For the same values of the non-dimensional speed and mass flow, the pressure ratio, the efficiency, and the choking mass flow were found to be significantly different for the three test gases. The experimental results have been found to be consistent with a CFD analysis of the impeller. Finally, it is shown that the changes in performance can be predicted reasonably well with simple arguments based mainly on one-dimensional isentropic flow. These arguments form the basis for correction procedures that can be used to project compressor characteristics measured for one value of γ to those for a gas with a different value.

Additional Metadata
Persistent URL dx.doi.org/10.1115/GT2002-30410
Conference ASME TURBO EXPO 2002: Controls, Diagnostics and Instrumentation, Cycle Innovations, Marine, Oil and Gas Applications
Citation
Roberts, S.K., & Sjolander, S. (2002). Semi-closed cycle O2/CO2 combustion gas turbines: Influence of fluid properties on the aerodynamic performance of the turbomachinery. Presented at the ASME TURBO EXPO 2002: Controls, Diagnostics and Instrumentation, Cycle Innovations, Marine, Oil and Gas Applications. doi:10.1115/GT2002-30410