Many gases, including carbon dioxide and argon, have been considered as alternative working fluids to air 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 $γ$ 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 nondimensionalized, 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 nondimensional speed, the pressure ratio, efficiency, and 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.

1.
Navaratnam
,
M.
, 1994, “
The Investigation of an Aero Derivative Gas Turbine Using Alternative Working Fluids in Closed/Semi Closed Cycles
,” M.Sc. thesis, Cranfield University, Cranfield, UK.
2.
Hunter
,
I. H.
, 1994, “
Design of Turbomachinery for Closed and Semi-Closed Gas Turbine Cycles
,” M.Sc. thesis, Cranfield University, Cranfield, UK.
3.
Zhou
,
M.
, and
Gauthier
,
J. E. D.
, 1998, “
A Literature Survey on the Use of O2∕CO2 Mixtures as the Primary Working Fluid in Combustion Engines
,” Mech. Eng. Report No. 980503,
4.
Mathieu
,
P.
,
Dechamps
,
P.
, and
Distelmans
,
M.
, 1994, “
Concepts and Applications of CO2 Gas Turbines
,” Technical Report,
Université de Liège
, Liège, Belgium.
5.
Ulizar
,
I.
, and
Pilidis
,
P.
, 1999, “
Handling of a Semiclosed Cycle Gas Turbine With a Carbon Dioxide-Argon Working Fluid
,” ASME Paper No. 99-GT-374.
6.
Jackson
,
J. B.
,
Neto
,
A. C.
,
Whellens
,
M. W.
, and
Audus
,
H.
, 2000, “
Gas Turbine Performance Using Carbon Dioxide as Working Fluid in Closed Cycle Operation
,” ASME Paper No. 2000-GT-153.
7.
Performance Test Code on Compressors and Exhausters, ASME PTC 10-1997.
8.
Kline
,
S. J.
, 1986,
Similitude and Approximation Theory
,
Springer-Verlag
, New York.
9.
Strub
,
R. A.
,
Bonciani
,
L.
,
Borer
,
C. J.
,
Casey
,
M. V.
,
Cole
,
S. L.
,
Cook
,
B. B.
,
Kotzur
,
J.
,
Simon
,
H.
, and
Strite
,
M. A.
, 1987, “
Influence of the Reynolds Number of the Performance of Centrifugal Compressors
,”
ASME J. Turbomach.
0889-504X,
109
, pp.
541
544
.
10.
Roberts
,
S. K.
, 2002, “
Effects of Fluid Properties on the Aerodynamic Performance of Turbomachinery for Semi-Closed Cycle Gas Turbine Engines Using O2∕CO2 Combustion
,” M.A.Sc. thesis, Carleton University, Ottawa, Canada.