556
15 Axial and Radial Turbines for Gases
Dependent dimensionless groups are expressed as functions of independent dimensionless groups according to
with γ being a constant for a given gas. If the Reynolds number is sufficiently large,
it does not constitute a strong condition for similarity. The preceding relation thus
mostly may be simplified to
15.3.2 Dimensionless Compressor and Turbine Characteristics
Performances characteristics do not change in general appearance when drawn in
dimensionless form. For compressors, charts may be as in Fig. 13.27 with pressure ratio and efficiency as functions of dimensionless mass flow rate for constant values of the dimensionless rotational speed. An alternative representation
is with efficiency by contour lines, as in Fig. 14.14. For turbines, the chart is
dimensionless mass flow rate as a function of pressure ratio for constant values of
dimensionless rotational speed (see Fig. 15.7). The chart may be completed with
efficiency as a function of pressure ratio. In practice, flow rate curves for various
rotational speeds are so close together that rendering the efficiency by contour
lines is not possible.
15.3.3 Corrected Quantities
Testing a compressor or a gas turbine ( D constant) generates characteristics depending on ambient pressure and temperature. This complicates the comparison of test
results performed under different atmospheric conditions. It is therefore advisable
to reduce characteristics to a standard temperature (e.g., 288.2 K) and a standard
pressure (e.g., 101.33 kPa). The real flow is then substituted by a dynamically similar flow, occurring under standard atmospheric conditions. According to the above
formulae, the following expressions should remain constant:
2
00
00
P
.
p D RT
00
03
2
00
00
00
m RT
p
D
f
,
, Re , ,
p
RT
p D
W
g
=
00
03
2
00
00
00
m RT
p
D
f
,
.
p
RT
p D
W
=
00
03
03
00
00
00
00
00
00
m RT
p T
P
,
,
,
,
, .
p
p T
RT
p
RT
W
h
15 Axial and Radial Turbines for Gases
Dependent dimensionless groups are expressed as functions of independent dimensionless groups according to
with γ being a constant for a given gas. If the Reynolds number is sufficiently large,
it does not constitute a strong condition for similarity. The preceding relation thus
mostly may be simplified to
15.3.2 Dimensionless Compressor and Turbine Characteristics
Performances characteristics do not change in general appearance when drawn in
dimensionless form. For compressors, charts may be as in Fig. 13.27 with pressure ratio and efficiency as functions of dimensionless mass flow rate for constant values of the dimensionless rotational speed. An alternative representation
is with efficiency by contour lines, as in Fig. 14.14. For turbines, the chart is
dimensionless mass flow rate as a function of pressure ratio for constant values of
dimensionless rotational speed (see Fig. 15.7). The chart may be completed with
efficiency as a function of pressure ratio. In practice, flow rate curves for various
rotational speeds are so close together that rendering the efficiency by contour
lines is not possible.
15.3.3 Corrected Quantities
Testing a compressor or a gas turbine ( D constant) generates characteristics depending on ambient pressure and temperature. This complicates the comparison of test
results performed under different atmospheric conditions. It is therefore advisable
to reduce characteristics to a standard temperature (e.g., 288.2 K) and a standard
pressure (e.g., 101.33 kPa). The real flow is then substituted by a dynamically similar flow, occurring under standard atmospheric conditions. According to the above
formulae, the following expressions should remain constant:
2
00
00
P
.
p D RT
00
03
2
00
00
00
m RT
p
D
f
,
, Re , ,
p
RT
p D
W
g
=
00
03
2
00
00
00
m RT
p
D
f
,
.
p
RT
p D
W
=
00
03
03
00
00
00
00
00
00
m RT
p T
P
,
,
,
,
, .
p
p T
RT
p
RT
W
h