ENHANCING THE RELIABILITY OF TURBOMACHINE CONDITION MONITORING EXPLOITING UNCONVENTIONAL RUGGED SENSORS
Creators: name: LANDI, ELIA
Publisher: name: Universit� degli Studi di Siena
Year: 2021

description: This work is focused on increasing the reliability of measurement systems for
turbomachine condition monitoring. The motivation stems from the fact that the
sensing systems that are widely used today to determine the behavior and health status
of turbomachinery use advanced methods such as digital twins.
A digital twin is a software representation of a physical device which relies on the data
coming from the onboard sensors and can be used to increase the reliability of the
device and to perform predictive maintenance to reduce the risk of costly failures.
In this framework, the sensors and the measurement systems must offer the highest
reliability. However, modern measurement systems rely on complex devices and
electronics which do not get along with the harsh environment present in a
turbomachine. In this work, the reliability enhancement of two of the main
measurement systems for turbomachine condition monitoring will be addressed.
The first analyzed measurement system is related to combustion monitoring with
particular reference to the detection of combustion chamber pressure oscillation
(pulsations). Typical pulsation monitoring techniques exploit piezoelectric sensors,
which are intrinsically robust devices, but suffer from problems related to wiring
robustness and, in general to the reliability of the electrical connections.
A novel measurement system for pressure oscillations in the combustion chamber,
which exploits pre-existing parts of the combustor, has been studied, realized and
tested in the field. In particular, the developed system is based on the measurement of
the ion density in the combustion chamber due to chemo-ionization, through the ion
current gathered by the electrode of the spare spark plug present in the combustor.
In this context, at first, a novel model of the ion current sensor and of the measurement
circuit was developed and used to predict and analyze the measurement technique
performance and to properly design the overall monitoring system. The model was
validated through experiments in laboratory. Finally, the proposed system was tested
in field in an industrial test rig.
The discussion continues with the improvement of turbomachine rotor dynamics
monitoring systems, with specific focus on torsional vibration detection. Measurement
systems for torsional vibration monitoring usually exploit capacitive sensing. Sensors
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are mounted in orifices in the stator case, which weaken the whole mechanical
structure. Moreover, also in this case, the wiring is a criticality.
In this work, the application to torsional vibration monitoring of preexisting variable
reluctance sensors normally used to monitor the turbomachine rotation speed has
been investigated. A novel system based on a special toothed wheel and on a tailored
front-end circuit was designed, realized and laboratory tested.
Also, in this case a model of the sensor and of the measurement circuit was developed
and used to analyze the potential of the proposed technique.
Summarizing, the aim of this work was to increase the reliability of two measurement
systems crucial for turbomachine condition monitoring, exploiting pre-existing
rugged components of the turbomachine itself. Two setups for the ion current
measurement and for the torsional vibration measurement were tested in the
laboratory obtaining satisfactory results: Moreover, the ion current measurement
system was tested in the field giving promising results when compared with the
performance of traditional pressure sensors.