The blade tip timing (BTT) measurement technique, first introduced in the late 1970s by the US Air Force and NASA laboratories, is now recognized as the most advanced method for measuring vibrations in axial turbomachinery blades. The fundamental principle involves determining the instantaneous blade tip deflection by measuring the deviations in the blade’s time of arrival at fixed angular positions. These time deviations—advances or delays—are detected using specialized proximity sensors mounted on the casing. BTT is widely employed for both validating the performance of new turbomachinery designs and for real-time condition monitoring in power plants, aircraft engines, and other applications.
A key advantage of BTT is its capability to measure the vibration of all blades using a limited number of sensors. This feature addresses the significant limitations of traditional resistance electrical strain gauges, which include localized measurement, complex wiring and signal transmission from rotating frames, potential alterations to the mass distribution of the rotor, and the reliance on complex inverse models to interpret tip displacement from measured deformations.
Currently, basic BTT measurement systems (BTTMS) are deployed by leading turbine manufacturers in the power generation (gas and steam) and aerospace industries. However, the calibration of BTTMS remains a critical challenge. Procedures for accurately estimating measurement uncertainty and ensuring traceability are not yet standardized. Addressing these gaps is essential for the effective certification, monitoring, and diagnostic use of BTTMS, ultimately enhancing operational safety. Blade vibration is a primary contributor to engine failure, and developing reliable calibration methods for BTTMS could significantly streamline the certification process, leading to substantial cost savings. Moreover, these advancements could enable new opportunities for condition-based engine maintenance.
In the long term, advancements in real-time onboard sensing of turbomachinery using BTT could facilitate the integration of Industry 4.0 and the Internet of Things (IoT) in aerospace and energy sectors.
This research project aims to develop innovative methods and technologies for calibrating BTTMS in response to the significant demand from turbine and aircraft engine manufacturers for metrological validation. The goal will be achieved by designing a novel test bench that utilizes kinematic inversion (where the blade remains rigid and the sensor undergoes controlled vibration). This approach builds upon previous research and existing equipment.
The successful development of this test bench will establish a scientific foundation for the future creation of international calibration standards and techniques for BTTMS, paving the way for future technology transfers and greater adoption in industry.