Handbook of Turbomachinery Second Edition Revised - Ventech!

pressure ratio [15]. It can be calculated directly from stage pressure and
temperature measurements:
Z ¼
1
TR 1
Pðg 1Þ=g
R
Likewise, for uncooled turbine stages, the efficiency is defined as the ratio of
actual work to the ideal work at a given pressure ratio:
Z ¼
1 TR
ðg 1Þ=g
1 PR Local Mach Number. Local flow Mach numbers can be calculated at any
position in the flow path where the total and static pressures and
temperatures are known. This can be done using the isentropic flow
relations:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
h i
1Þ=g
M ¼ Pðg
R 1
g 1
The specific heat ratio is a function of temperature.
Data Presentation
Performance Maps
The customary method of presentation for turbomachine stage performance
characteristics are the maps described in the first section. Two sets of data
are normally presented, which completely describe the stage aerodynamic
performance. These include a family of corrected constant-speed lines with
stagnation pressure and temperature ratios plotted as a function of
corrected flows. Stage adiabatic efficiency is calculated as a function of
measured pressure and temperature ratios or from torque meter measurements.
Stall Margin Definitions
A measure of great interest to turbomachine designers is the fan and
compressor stall margin. It is a measure of performance margin between a
stage operating point and the stall line. Often, stage performance
specifications will include a stall margin requirement. There are at least
two well-accepted definitions for stall margin, constant-speed line stall
margin and constant-flow stall margin.
Copyright © 2003 Marcel Dekker, Inc.