In turbomachinery, engine vibrations play an essential role, since they may lead to a fast component degradation, lowering the performance and ultimately yielding to fatigue damage. For these reasons, there is a high demand for measurement methods to monitor the behavior of the engine shaft adequately. In this experiment, we characterize the shaft behavior of a turbomachine by measuring the blade tip clearance and by converting it to a shaft displacement. To achieve this goal, we have employed two optical displacement sensors and we have applied the full spectrum technique.
The design and performance evaluation of an innovative, small size, compactly packaged high temperature interferometric optical sensor for harsh environments is reported. The sensor was built with a short segment of strongly coupled multi-core optical fiber (MCF) spliced to a typical single mode fiber (SMF). Matlab MathWorks and PhotonDesign simulation programs were used to design the sensor to monitor the widest temperature range possible with a commercial sensor interrogator. The SMF-MCF structure was protected by two temperature-resistant tubes: an inner ceramic tube with an internal hole that matched the MCF diameter in order keep it tightly in axial direction to avoid the effects of bending and/or vibrations that could be misinterpreted as temperature measurements, and an outer metallic tube to provide protection against impacts. The calibration of our packaged MCF sensor was carried out in a high temperature furnace at the facilities of the Aeronautical Technologies Center (CTA) and a calibrated standard K-type thermocouple was used as a reference. The calibration was performed repeatedly in the range from 200 to 950 °C and the gathered spectra were processed entirely by a custom program made in Matlab MathWorks. Our sensor responded lineally in the tested range with an average temperature sensitivity of 29.1 pm/°C and showed high robustness against vibrations. Results indicate that our MCF sensor is as accurate as the K-type thermocouple with the advantage of its appropriate passiveness for harsh environmental industrial applications.