Blade tip clearance and time of arrival immediate measurement method using an optic probe

Abstract

The measurement of the tip clearance and the time of arrival of every single blade in rotating turbo machinery is the starting point to characterize the performance of a rotating turbine. The type of sensors employed to acquire the data for this analysis are mainly non-intrusive such as optic, capacitive, eddycurrent and microwave sensors. This paper introduces the method employed to calculate the tip clearance and time of arrival of the blades using a fibre-optic probe. The time of arrival of each blade is evaluated right after detecting its pass, and before the next blade finishes passing in front of the sensor. Both parameters are available from that moment for further analyses by a post-processor device. During the acquisition of the sensor data, the maximum and minimum tip clearance and time of arrival are also computed for the current measurement and their values are also made available for post-processing. The whole algorithm has been developed in a single core using a hardware description language and implemented on a programmable logic device which allows for easy extension of the system when more than one sensor monitoring is required.

A review of blade tip clearance–measuring technologies for gas turbine engines

“…[63][64][65] Based on past results, they applied the reflected intensity-modulated optical fiber sensor for the health monitoring of engine by measuring real-time tip-timing and tip-clearance measurements, and the tipclearance measurement for the first stage of an aircraft engine's compressor was carried out using the optical fiber sensor; its main component was a tetra-furcated bundle of optical fibers, with which the resulting precision of the experimental measurements could reach 12 mm. [66][67][68] Recently, they carried out experimental researches on the vibrational behavior of a rotating disk by three optical fiber sensors, which demonstrated the suitability of this innovative optical system to characterize rotating disks in simulated working environments of the engine. Using this sensor, not only the amplitude and frequency of the vibration but also the number of nodal diameters of the disk and its variations during the tests can be identified.…”

A Review of NDT/Structural Health Monitoring Techniques for Hot Gas Components in Gas Turbines

“…In-situ tip clearance measurements with laser doppler method were presented by Büttner et al [50,51]. Gil-García et al [52] and Zielinski et al [53] focused their work on time of arrival measurements on compressor and turbine blades, to determine blade vibration. Overton developed an LDV system to measure tip clearance more accurately, compared to the capacitive method [54].…”

Architecture for Measuring Blade Tip Clearance and Time of Arrival with Multiple Sensors in Airplane Engines

“…The features of an FPGA are also suitable to scale the processing to many sensors. The sequential algorithms designed in MATLAB to detect the change of blade have been redesigned to be adapted to the nature of the FPGA technology [21]. Figure 3 shows the block diagram of the TC and ToA processor.…”