in compressor characteristic. It is also worthy to note that in further research of
control method, the improvement of the compressor stability is not necessarily
targeted by sizable extension of the stability boundary. Instead, the ability of
compressor systems to remain stable in the face of external disturbances is perhaps
more practical. This concept, called operability enhancement of the compressor,
was given in its clear and detailed description in Ref. [3, 48]. Technically, it could
mean that the control power needed is only for the disturbance rejection at very
early stage, any time when the external disturbance emerges, but not for the
suppression of grow-up disturbances, i.e. no ability to drag the compressor back
if it has already fallen into stall. It is hoped that in doing so, the expense of control
power and the complexity of control system could be largely reduced.
Conclusions.
Revitalized development in researching the compressor flow
instability and its control has been described. It is hoped to be able to shed some
light on the persevering efforts of research and development in attempting to break
the barrier for the stable operation of compressors, the innovative approaches
emerged in the course of these efforts, and the future perspectives towards the
goal of stability enhancement.
In parallel with the emerging technology of active control, the research on the
pre-stall behavior has been in the central attention for many years concentrating
on the inception period immediately prior to final stall. The main outcome of the
research lies in its ability to demonstrate the interplay between the system mode
and the flow event on the scale of blade passages, resulting to different types
of stall precursors and different control approaches. This understanding could be
further extended if the behavior in the early pre-stall period can be clarified and
included into the modeling and experiment work.
Fig. 3. Unsteady velocity patterns in full annulus of compressor blade row computed
at the same compressor flow rate for the cases with and without micro injection
showing the stability enhancement under micro injection
122 ISSN 0236-3941. Вестник МГТУ им. Н.Э. Баумана. Сер. “Машиностроение”. 2006. № 2
