Optical Interferometer for Turbine Blade Tip Clearance Measurement
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Solution Overview
Problem
Current technologies lack a reliable, real-time method to accurately measure blade tip clearance in gas turbines, especially considering the abradable layer's wear, which affects efficiency and requires complex electronic circuits difficult to implement in engine environments.
Innovation Solution
The use of optical interferometers, such as Fabry-Perot or Michelson, combined with optical fibers embedded in the abradable substrate, to measure blade tip clearance by analyzing interference patterns and fiber abrasion, providing a non-electronic, high-temperature tolerant solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If optical intensity-based measurement methods are used to measure blade tip clearance, then the measurement can be performed remotely, but the measurement accuracy deteriorates due to long-term changes in light launch, reflectivity changes, light losses, and other factors
Solution Approach 1:
The patent replaces intensity-based optical measurement with interferometric measurement. Instead of measuring light intensity which is susceptible to environmental changes, the system uses interference patterns created by coherent light sources to measure clearance. The interferometer creates a reference beam and a measurement beam that recombine to produce interference patterns, allowing precise measurement of blade tip clearance relative to the abradable layer while being immune to long-term drift and environmental variations.
Solution Approach 2:
The patent introduces an interferometer as an intermediary measurement system between the light source and the blade tip. The interferometer processes the optical signals through interference pattern generation, converting the physical clearance measurement into an interference pattern that can be analyzed with high precision. This intermediary device eliminates the direct dependence on light intensity and provides a more stable measurement reference.
2Measurement precision
If conventional optical measurement systems are used, then the measurement can be performed, but the measurement does not accurately account for abradable layer wear, resulting in incorrect clearance values
Solution Approach 1:
The patent incorporates the abradable layer into the measurement system by positioning the interferometer to measure clearance relative to the abradable layer surface. The system performs preliminary measurement of the abradable layer surface position and uses this as a reference. By doing so, the measurement automatically accounts for wear of the abradable layer, providing accurate clearance values that reflect the actual operating conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the interferometer continuously monitors the clearance between the blade tip and the abradable layer. The measurement system processes interference patterns to determine clearance changes in real-time, providing feedback that accounts for abradable layer wear. This feedback loop ensures that the clearance measurement always reflects the current state of the abradable layer and blade tip relationship.
3Measurement precision
If rub pin structures with electrical wires are used to detect abradable layer wear, then wear measurement is possible, but the system requires high temperature electronic circuitry that is difficult to implement
Solution Approach 1:
The patent replaces the electrical circuit-based rub pin structure with an optical interferometer system. Instead of using electrical wires and electronic circuits to detect wear, the system uses optical interference patterns to measure the position of the abradable layer surface. This substitution eliminates the need for high-temperature electronic circuitry while maintaining the ability to detect abradable layer wear with high precision.
Solution Approach 2:
The patent introduces an optical interferometer as an intermediary measurement device that replaces the electrical detection system. The interferometer uses optical fields instead of electrical circuits to detect wear. By measuring interference patterns of light reflected from the abradable layer surface, the system achieves wear detection without requiring high-temperature electronic components, significantly simplifying the overall system implementation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate, real-time measurement of blade tip clearance relative to the abradable layer, improving efficiency by accounting for wear and eliminating the need for high-temperature electronic circuitry, thus enhancing operational reliability.
Implementation Method 1
a Fabry-Perot optical interferometer... light transmitted and reflected through the optical cavities by reflection off of the different surfaces of the outer blade tip and the window creates an interference pattern
Implementation Method 2
an optical time-of-flight measurement system... the blade tip clearance can be measured by a time of flight of optical energy of the emitted and reflected light
Implementation Method 3
an enhanced system that employs a rub pin configuration for detecting and measuring abradable layer wear using optical fibers
Data Source
AI summary
A blade tip measurement system includes a case and a blade that rotates within the case, the blade having an outer blade tip surface that has a clearance distance from an inner surface of the case. A light source emits light along an optical path that is directed toward the outer blade tip surface by a lens, and the outer blade tip surface reflects the light back along the optical path. An optical interferometer generates an interference pattern using the reflected light, and a photoreceiver receives the interference pattern. A complex logic device determines the clearance distance of the blade tip surface from the inner surface of the case based on the interference pattern. The interferometer may be a Fabry-Perot optical interferometer formed using a window positioned between the lens and the blade tip surface, or a Michelson interferometer formed using a reference optical path. The system may alternatively include an optical time of flight measurement of the blade tip clearance. The system further may include an abradable substrate having an optical fiber array of optical fibers at different depths, whereby the blade tip clearance is determinable based on which of the optical fibers are abraded as the blade tip rotates.