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TECHNICAL PAPERS: Gas Turbines: Aircraft Engine

Experimental Operating Range Extension of a Twin-Spool Turbofan Engine by Active Stability Control Measures

[+] Author and Article Information
Stephan G. Scheidler

Institut für Strahlantriebe,  Universität der Bundeswehr München, D-85577 Neubiberg, Germanystephan.scheidler@unibw-muenchende

Leonhard Fottner

Institut für Strahlantriebe,  Universität der Bundeswehr München, D-85577 Neubiberg, Germany

J. Eng. Gas Turbines Power 128(1), 20-28 (Mar 01, 2004) (9 pages) doi:10.1115/1.2031247 History: Received October 01, 2003; Revised March 01, 2004

Modern engine operation is guided by the aim to broaden the operating range and to increase the stage loading allowing the stage count to be reduced. This is possible by active stability control measures to extend the available stable operating range. Different strategies of an active control system, such as air injection and air recirculation have been applied. While in the past results have been published mainly regarding the stability enhancement of compressor rigs or single-spool engines, this experimental study focuses on both the stability as well as the operating range extension of a twin-spool turbofan engine as an example of a real engine application on an aircraft. The objective of this investigation is the analysis of the engine behavior with active stabilization compared to unsupported operation. For this purpose, high-frequency pressure signals are used and analyzed to investigate the effects of air injection with respect to the instability onset progress and the development of any instabilities, such as rotating stall and surge in the low-pressure compression (LPC) system. These Kulite signals are fed to a control system. Its amplified output signals control fast acting direct-drive valves circumferentially distributed ahead of the LPC. For the application of air injection described in the paper, the air is delivered by an external source. The control system responsible for air injection is a real-time system which directly reacts on marked instabilities and their precursors. It allows the LPC System to recover from fully developed rotating stall by asymmetric air injection based on the pressure signals. Additionally, a delayed appearance of instabilities can be provoked by the system. Air injection guided by this control system resulted in a reduction of the required amount of air compared to constant air injection. Also, disturbances travelling at rotor speed can be detected, damped, and eliminated by this control system with a modulation of the injected air in such a way that the injection maximum travels around the ten injection positions.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cutaway model of the LARZAC 04 C5 turbofan engine

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Figure 2

Bypass and core throttle devices

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Figure 3

Air injection system with pivoted nozzles

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Figure 4

Comparison of air injection nozzle exit area design

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Figure 5

Screw compressor, air dryer, and storage vessels

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Figure 6

Direct drive valve by the Moog Company, Germany

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Figure 7

Engine test setup in air injection configuration

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Figure 8

Conventional low-frequency instrumentation

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Figure 9

Position of high-frequency instrumentation

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Figure 10

Disturbance at rotor frequency frot,nθLPC=78%

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Figure 11

Time series of sensor signals and valve No. 1 at nθLPC=78%

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Figure 12

Comparison of constant and controlled air injection, valves opened 30%, at nθLPC=78%

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Figure 13

Several opening degrees of the valves at constant air injection for nθLPC=84%

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Figure 14

Comparison of constant and controlled air injection, valves opened 30%, at nθLPC=84%

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Figure 15

Stabilizing effect of air injection, also at unthrottled operation at nθLPC=84%

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Figure 16

Restabilization of the LPC after two instability occurrences, at nθLPC=84%

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Figure 17

Comparison of constant and controlled air injection, valves opened 30%, at nθLPC=90%

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Figure 18

Restabilization of the LPC after an instability occurrence, at nθLPC=90%

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Figure 19

Time series of sensor signals and valve No. 1 at nθLPC=90%

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Figure 20

SFT of the first-harmonic and second-harmonic order for nθLPC=90%

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Figure 21

PSD of the first-harmonic, disturbance at rotor frequency, (frot), at nθLPC=90%

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Figure 22

PSD of the first-harmonic, disturbance at rotor frequency (frot) damped, at nθLPC=90%

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