Handbook of Turbomachinery Second Edition Revised - Ventech!

These measurements include radial surveys directly behind the rotor, wake
rake measurements behind fixed blades and struts, boundary-layer probes to
measure profiles in the boundary layer, dynamic pressure sensors located
near the rotor for stall/surge indications, and tip clearance probes to
measure in real time the running blade-tip clearance.
Total pressure, temperature, and yaw (circumferential) and pitch
(radial) absolute flow angles at the rotor exit plane can be measured with
yaw-nulling probes, which are traversed radially across the flow path. Wake
rakes consist of a series of pressure taps mounted on a fixture such that a
circumferential spatial pressure distribution is measured across the flow path
at a fixed radius. Wake rakes can be mounted on radial survey mechanisms
so that wake profiles can be recorded across the flow path.
High-response pressure transducers flush mounted in the vicinity of
the rotor blade tip are used to measure unsteady static pressures on the flow
duct outer casing. These data can be monitored to identify flow separation
and shock waves on the rotor blade tip.
Rotor blade-tip clearance differences can impact stage performance,
especially in compressors and fans. Typically, stage pressure rise and
efficiency decreases with increased blade-tip–shroud clearance [10]. Test rigs
usually include dynamic proximity sensors to measure rotor tip clearances
during testing. Sensors are mounted circumferentially over the blade tips,
flush to the outer flow path.
Not shown in Fig. 4but equally important is the instrumentation
required for flow rate and test rig speed measurements. Often a torque meter
is used to measure test rig power consumption or generation.
Instrumentation also required but not discussed in this chapter
includes that required to monitor in real time the mechanical health of the
test rig and test facility during test rig operations.
Instrumentation Planning and Layout
The previous section identified the measurements required for turbomachinery
aerodynamic performance testing. In this section we discuss the
methodologies for placing and locating the instrumentation on the test rig.
Total Pressure Measurements
Stage pressure ratios are calculated using averaged pressures measured from
both the inlet and discharge total pressure rakes. An understanding of where
the inlet and discharge total pressure rakes are located in the test rig relative
to the stage blading is important in the total system performance analysis of
gas turbine machines. Unless corrected for, the measured stage pressures
Copyright © 2003 Marcel Dekker, Inc.