
100
AIRCRAFT ENGINE DESIGN
Table 4.2 Calling nomenclature for subroutine FAIR
Symbol Knowns Unknowns
FAIR(l, f, T, h, Pr, 4), Cp, R, y,a) f, T h, P~, (]), Cp, R, y,a
FAIR(2, f, T,h, Pr, c]),Cp, R, y,a) f,h T, Pr, 4),Cp, R, y,a
FAIR(3, f, T,h, P~,c]),Cp, R, y,a) f, Pr
T,h, qb, Cp,
R, y,a
FAIR(4, f, T,h, P,.,qS, Cp, R, y,a) f, q5 T,h, Pr, Cp, R, y,a
b) Eq. (4.3f) becomes the familiar isentropic relationship
(-~l)s=const=(~l) Y-zzT-I (4.3f-CPG)
The effect of variable gas properties can be easily included in a computer analysis
of gas turbine engine cycles, as follows. In addition to the ideal gas equation, two
subroutines are needed: 1) a subroutine that can calculate the thermodynamic state
of the gas given the fuel/air ratio f and one temperature dependent property; and
2) a subroutine that can calculate the compressible gas relationships Tt/T, Pt/P,
and mass flow parameter (MFP) given the Mach number (M), total temperature
(Tt), and fuel/air ratio (f).
The subroutine FAIR was developed to calculate the temperature dependent
properties given the fuel/air ratio f and one of the following properties: T, h,
Pr, or ~p. Table 4.2 gives the calling nomenclature for the subroutine FAIR. The
subroutine also determines the specific heat Cp, the gas constant R, the ratio of
specific heats V, and the speed of sound a.
The compressible flow subroutine RGCOMP was developed to calculate the
compressible flow relationships for this gas model with variable specific heats.
Table 4.3 gives the calling nomenclature for this subroutine. The equations used
in RGCOMP are given in Appendix F.
4.2.3 Total Property Ratios
You will find it very important to be able to swiftly identify and thoroughly
grasp the physical meaning of the quantities that are about to be defined in order
to understand and manipulate the cycle analysis results. We therefore recommend
that you spend enough time to completely familiarize yourself with the material
Table 4.3 Calling nomenclature for subroutine RGCOMP
Symbol Knowns Unknowns
RGCOMP(1, T,, f, M, T,/T, Pt/P, MFP)
RGCOMP(2, Tt, f, M, TilT, P,/P, MFP)
RGCOMP(3, Tt, f, M, Tt/ T, Pt/ P, MFP)
RGCOMP(4, T,, f, M, T,/T, P,/P, MFP)
RGCOMP(5, Tt, f, M, Tt/ T, P,/ P, MFP)
Tr, f,M Tr/T, Pt/P, MFP
Tr, f, Tt/T M, Pt/P, MFP
T,,f, Pt/P M, Tt/T, MFP
T,,f, MFP T,/T, Pt/P,M < I
T,,f, MFP Tt/T, Pt/P,M > 1