In order to preserve fossil resources aviation industry faces
major challenges to reduce engine fuel consumption. Therefore
efforts are concentrated to increase efficiency of any engine component.
Investigations at the Institute of Jet Propulsion at the
University of Federal Armed Forces in Munich focus on the compressor
module. Especially the compression system of a gas turbine
is designed to operate at very high aerodynamic loads. This
makes it one of the most critical components during transient engine
operation or inlet flow distortion. Rotating stall and surge
have to be avoided in any situation during engine operation. For
this reason a detailed knowledge of the flow phenomena of the
compressor in normal conditions as well as near the stability
limit is essential. Often those research activities are carried out
at compressor rigs but not in by utilizing real turbo engines.
As a research test vehicle at the Institute of Jet Propulsion the
Larzac 04 C5 twin-spool turbofan engine is operated at the engine
test facility. The gas turbine is equipped with additional
instrumentation and control systems exceeding those of conventional
engine monitoring systems by far. Especially a set of high
frequency pressure transducers has been installed above the tip
of the first stage of the low pressure compressor in order to investigate
tip flow phenomena. Besides the information on the
flow phenomena in the tip region of the compressor blades these
signals can also be used to detect the upcoming of rotating stall
precursors. A special algorithm which was developed at the institute
is able to estimate the stall and to trigger an active countermeasure.
This was demonstrated successfully for a wide range
of operating points.
Stall inception in different speed ranges is crucial to be detected
reliably. More than all high spool speeds challenge an active
stabilization system. With the stall typically rising in time periods
of less than three rotor revolutions, the requirements regarding
high speed data processing are enormous. Since computer
technology now provides systems, which are capable to handle
such a task and still are compact and robust enough to be used
in the rough environment of engine test beds, the challenge remains
to set up fitting actuator systems. The test vehicle at the
Institute of Jet Propulsion is therefore equipped with fast acting
valves, which feed an injector casing mounted closely upstream
of the low-pressure compressor. Test series have been performed,
which proof the stabilizing capabilities of the entire system. Even
at high spool speeds the stall was sufficiently suppressed and a
stable operation of the engine was guaranteed.
«