Handbook of Turbomachinery Second Edition Revised - Ventech!

ought to rest isentropically. Total pressure and temperature measurements
are made with sensors that stagnate the flow at the point of interest in
the flow field. Very accurate total pressure and temperature measurements
can be made with well-designed sensors. Other instrumentation illustrated in
Fig. 4is used to support flow-field definition and performance diagnostic
analysis.
Even though the flow paths and blading characteristics are considerably
different for single and multistage fans, axial and cetrifugal
compressors, and turbines, the performance measurement requirements
and techniques are essentially the same for each of these turbomachine
components.
The total pressure increase/decrease across the stage of interest is
measured using total pressure sensors located at specific streamwise stations
relative to the blading. An accurate measurement requires that both inlet
and exit total pressures be recorded. As seen in Fig. 4, inlet total pressures
are recorded with radial immersion rakes located just upstream of the stage
of interest. This normally includes multiple individual rakes, which are
equally spaced around the circumference.
Stage exit total pressures are also measured with multiple radial
immersion rakes located downstream of the stage exit plane. Total
temperatures across the stage are measured with thermocouple temperature
sensors mounted on radial immersion rakes. The change in total
temperature across the stage coupled with the stage pressure ratio can be
used to calculate stage adiabatic efficiency and aerodynamic power
requirements.
Static pressure taps, mounted flush to both the inner and outer flow
path walls, are installed throughout the test rig. Typical locations are seen in
Fig. 4. Static pressures measured in conjunction with total pressures and
temperatures can be used to calculate local flow velocities. In addition, static
pressure taps can be located at rotor and stator leading and trailing edges on
both the hub and shroud, completely around the flow-path circumference.
Circumferential static pressure distributions are a good indication of flow
velocity uniformity. Uniform static pressures suggest uniform velocities,
whereas nonuniform static pressures indicate nonuniform velocities.
A row of static pressure taps is often placed at midpassage between
two of the stator blades along both the hub and tip shrouds. These
measurements provide a quantitative assessment of the static pressure
changes across the stator assembly. Other static pressure taps are located at
stationary and traversing measurement planes.
In addition to instrumentation requirements for performance measurements,
the engineer will often instrument the test rig to acquire specific
test data that can be used for blade-row performance diagnostic purposes.
Copyright © 2003 Marcel Dekker, Inc.