Blade Tip Timing Probe for Axial Displacement Measurement
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Solution Overview
Problem
Current methods for determining rotor blade axial displacement in gas turbine engines, particularly in high-pressure turbine stages with short axial blade tips, are limited by the inability to mount multiple probes due to stress and thermal constraints, leading to incomplete measurement of blade tip axial displacement and lack of real-time feedback.
Innovation Solution
A method using a single axial probe location with a rotor blade featuring a once-per-revolution feature and two measurement features arranged at an acute angle, allowing for the calculation of blade untwist angle and axial displacement based on time-of-arrival measurements from a stationary timing probe, enabling real-time monitoring with minimal computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple blade tip timing probes are mounted around the rotor stage, then measurement accuracy of blade tip axial displacement is improved, but device complexity and weight increase
Solution Approach 1:
The blade tip is segmented into multiple measurement features (first measurement feature and second measurement feature) that can be detected by a single probe. This segmentation allows the system to extract multiple measurement points from one probe location, effectively achieving multi-point measurement capability without requiring multiple physical probes.
Solution Approach 2:
The measurement approach transitions from purely axial displacement measurement to include circumferential position information. By detecting the circumferential position of measurement features around the blade tip and combining this with axial timing data, the system can calculate both axial displacement and blade untwist angle using trigonometric relationships, effectively adding a circumferential dimension to the measurement capability.
2Productivity
If multiple probes are mounted on the casing to measure blade tip timing, then real-time monitoring capability is improved, but weight and structural complexity increase
Solution Approach 1:
A single stationary timing probe is designed to perform multiple measurement functions: detecting the once per revolution feature for rotational synchronization, detecting the first measurement feature for axial displacement measurement, and detecting the second measurement feature for blade untwist measurement. This multi-functional probe eliminates the need for multiple specialized probes while maintaining comprehensive monitoring capability.
Solution Approach 2:
The blade tip structure itself provides the measurement features (ridges, grooves, or lines) that serve as the measurement targets. The blade's own geometry is utilized to create the measurement references, eliminating the need for separate measurement devices attached to the blade, thereby reducing overall system weight and complexity.
3Measurement precision
If probes are mounted on shroud segments to measure blade tip position, then measurement capability is improved, but manufacturing difficulty increases due to stress and thermal constraints
Solution Approach 1:
The measurement features (ridges, grooves, or lines) are pre-formed as integral parts of the blade tip manufacturing process. These features are created during blade fabrication rather than being added afterward, ensuring they are properly integrated into the blade structure and can withstand the same stress and thermal conditions as the blade itself, eliminating manufacturing conflicts between probes and shroud segments.
Solution Approach 2:
The measurement features act as intermediaries between the blade tip and the stationary probe. Instead of directly mounting probes to the shroud segments (which creates manufacturing and thermal problems), the measurement features on the blade tip serve as the direct measurement interface, allowing the stationary probe to measure blade position without requiring any modification to the shroud segment structure.
4Device complexity
If a single probe is used to measure blade tip timing, then device complexity is reduced, but measurement completeness deteriorates due to insufficient axial length on shroud segments
Solution Approach 1:
The blade tip is segmented into multiple measurement features (first measurement feature and second measurement feature) arranged at an acute angle. This segmentation allows a single probe to detect multiple distinct features during one revolution, extracting multiple measurement parameters (axial displacement and circumferential position) from a single probe location, thereby preventing information loss despite using only one probe.
Solution Approach 2:
The measurement features are arranged to be sequentially detected during blade rotation, with the once per revolution feature providing rotational synchronization and the measurement features providing continuous axial and circumferential position data. This continuous detection throughout the rotation ensures complete measurement information is captured without requiring multiple probes.
Data Source
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AI summary
A method of determining rotor blade axial displacement (b ij ). The rotor blade tip (34) comprises first and second measurement features (36, 38) arranged to make an acute angle therebetween. Measure time of arrival (t ijk ) of the once per revolution feature (1), first and second edges (40, 42) of the first measurement feature (36), and first and second edges (44, 46) of the second measurement feature (38), for at least two revolutions of the rotor (2). Convert these to circumferential distances (d ijk ) for each revolution. Calculate a feature angle (± ijk ) between each measurement feature (36, 38) and the once per revolution feature (1) for each revolution. Calculate blade untwist angle (Õ ij ) from the change in feature angle (± ijk ) between measured revolutions. Calculate the rotor blade axial displacement (b ij ) from the blade untwist angle (Õ ij ) and the circumferential distance (d ijk ) of the point from one of the measurement features (36, 38).