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Active stabilization to prevent surge in centrifugal compression systemsThis report documents an experimental and analytical study of the active stabilization of surge in a centrifugal engine. The aims of the research were to extend the operating range of a compressor as far as possible and to establish the theoretical framework for the active stabilization of surge from both an aerodynamic stability and a control theoretic perspective. In particular, much attention was paid to understanding the physical limitations of active stabilization and how they are influenced by control system design parameters. Previously developed linear models of actively stabilized compressors were extended to include such nonlinear phenomena as bounded actuation, bandwidth limits, and robustness criteria. This model was then used to systematically quantify the influence of sensor-actuator selection on system performance. Five different actuation schemes were considered along with four different sensors. Sensor-actuator choice was shown to have a profound effect on the performance of the stabilized compressor. The optimum choice was not unique, but rather shown to be a strong function of some of the non-dimensional parameters which characterize the compression system dynamics. Specifically, the utility of the concepts were shown to depend on the system compliance to inertia ratio ('B' parameter) and the local slope of the compressor speedline. In general, the most effective arrangements are ones in which the actuator is most closely coupled to the compressor, such as a close-coupled bleed valve inlet jet, rather than elsewhere in the flow train, such as a fuel flow modulator. The analytical model was used to explore the influence of control system bandwidth on control effectiveness. The relevant reference frequency was shown to be the compression system's Helmholtz frequency rather than the surge frequency. The analysis shows that control bandwidths of three to ten times the Helmholtz frequency are required for larger increases in the compressor flow range. This has important implications for implementation in gas turbine engines since the Helmholtz frequencies can be over 100 Hz, making actuator design extremely challenging.
Document ID
19930009673
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Epstein, Alan H. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Greitzer, Edward M. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Simon, Jon S. (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Valavani, Lena (Massachusetts Inst. of Tech. Cambridge, MA, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Subject Category
Mechanical Engineering
Report/Patent Number
NASA-CR-191625
NAS 1.26:191625
Accession Number
93N18862
Funding Number(s)
CONTRACT_GRANT: NAG3-770
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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