More Intelligent Gas Turbine Engines - FTP Directory Listing - Nato

ACTIVELY CONTROLLED COMPONENTS
big enough to be restrained by the damper. This restriction makes them unsuitable for small and high
frequency vibration modes (e.g. chord-wise modes).
Active vibration control (AVC) could help to overcome design restrictions induced by resonant vibrations
during the operating range. When applying AVC, vibrations within the operating range could be accepted and
open new spaces for improved aerodynamic blade design concepts. The development of active damping
systems allows damping devices to cope with small vibration amplitudes and expands the range of usability of
damping devices. Active devices can be introduced as an additional part or even be integrally installed on the
component, e.g. casted with airfoils.
The advantages of active damping systems are:
• Lower weight of the components because of less design restrictions;
• Acceptance of critical resonance within operating range, that leads amongst others to more effective
aerodynamic design that produces resonant profiles;
• Noise reduction; and
• Reduction of damage during stall condition.
The following disadvantages arise:
• A current generator is necessary; and
• Additional electronics create more complex systems, which leads to lower reliability.
One promising active damping line is the use of piezoelectric elements or other material/physical phenomena
that dissipate energy. These elements transform the mechanical energy in electrical energy, so attenuating the
vibratory amplitude. The approach has been successfully developed for aeronautic structures (wings),
however its application in an engine is not possible yet due to restrictions in operating temperature and
pressure/deformation range.
Due to the better availability and the increased capacity of electrical power of the next generation aero engine
(so-called “more electric engine”) some advanced design concepts to improve the rotor dynamical behavior of
aero engines are studied now again. Different level complexity – from pure passive to full authorized systems
– is considered with the strong focus on aero engines (see references [2.63]-[2.73]).
2.3.3 Combustor
2.3.3.1 Introduction
Active combustion instability control (AIC) manipulates combustion behavior using a dynamic hardware
component (actuator) that rapidly modifies an input into the combustion process. In closed-loop control a
sensor is monitoring the combustor output in real time to determine actuator action via control algorithms.
Adaptive control refers to a self-adjusting controller that can modify the controller action depending on the
transient external circumstances.
Initial AIC combustor experiments were motivated to control combustion instabilities in aero engine
augmenters. More recently the instability control has been focused on very-low emissions stationary gas
turbines and will become critical for future aero engines with operation near lean blow-out limits. AIC is also
being explored for reducing non-uniformities of turbine entrance temperature distribution (reduce pattern
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