During the development process as well as the entire
lifecycle of aircraft engines extensive testing is required for
validation / certification and for maintenance purposes. For this
reason various engine test facilities are operated in industry and
research institutes. Some of those are indoor test beds which
could suffer several deficits concerning the test cell depression
or the entrainment ratio. Both are mainly driven by the ejector
pump effect that establishes at the detuner inlet of the facility.
At the Institute of Jet Propulsion at the University of the
German Federal Armed Forces an indoor test bed capable of
thrust levels up to 50kN is operated for research as well as
academical purposes. Therein engines of different types are
operated sometimes even under off design conditions beyond
the stability limits. Therefore the knowledge of the flow
conditions, which are induced by the facility itself, is of
particular importance and they have to be considered in detail.
Among stability problems of the gas turbine related to those
aerodynamic conditions the test cell depression is a major
parameter as it is responsible for the loads onto the facilities
statics. Basic research on the field of ejector pump effects in
engine test facilities was therefore performed at the institute in
the past. But measuring enough data in order to characterize the
entire flow conditions inside the test bed or simulating a facility
of this kind requires major time and cost efforts and is therefore
typically limited to some specific sections. For this reason a
scaled model has been build to investigate the basic effects
establishing inside the test cell. A jet engine for model aircrafts
is operated in the test bed to generate the primary air flow. The
scaled model offers the possibility to apply a wider range of
measurement techniques than it would be possible inside the
large facility. Therefore a large amount of data can be provided
for adequate CFD validation purposes. The paper will address
the main geometrical parameters of this test bed which take
affect on the ejector pump effect. With several changes of the
test setup, e.g. variation of detuner location, an insight into the
specific flow phenomena during engine testing can be
achieved.
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