Distributed Fiber Optic Sensing for Gas Turbine Housing Displacement
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Solution Overview
Problem
Current methods for measuring gas turbine engine housing displacement and temperature during operation are inaccurate and time-consuming, as they rely on photogrammetric techniques that fail to differentiate between strain and temperature influences, and do not provide real-time data.
Innovation Solution
A distributed fiber optic sensing system using optical frequency domain reflectometry (OFDR) is coupled to the turbine engine housing, with a temperature sensor to separate temperature influences from strain measurements, enabling real-time monitoring of dynamic strain, displacement, and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If photogrammetric techniques are used to measure engine housing displacement, then measurement coverage is obtained, but measurement precision deteriorates due to inability to differentiate between strain and temperature influences
Solution Approach 1:
The patent segments the measurement function by deploying multiple optical fibers at different locations and orientations on the engine housing. Each fiber measures local strain, and the system integrates these segmented measurements to reconstruct overall displacement while compensating for temperature effects, thereby maintaining precision across the entire housing surface.
Solution Approach 2:
The patent introduces temperature sensors and unrestrained optical fibers as intermediary elements to measure temperature independently. These intermediaries provide temperature data that is then used to compensate for thermal effects in the strain measurements, enabling accurate displacement measurement despite temperature variations.
2Device complexity
If traditional displacement measurement methods are used, then measurement process is simple, but measurement precision deteriorates due to conflation of strain and temperature effects
Solution Approach 1:
The patent merges multiple measurement functions into a unified system where optical fibers measure both strain and temperature effects simultaneously. By combining data from multiple fibers and integrating temperature compensation, the system achieves precise strain measurement while maintaining manageable complexity through automated data processing.
Solution Approach 2:
The patent changes the measurement parameters by transitioning from direct displacement measurement to indirect strain measurement via optical fibers. The system measures frequency shifts in optical signals that correspond to strain and temperature, then transforms these parameters into compensated strain values through mathematical processing.
3Productivity
If real-time monitoring is implemented, then productivity is improved, but device complexity increases due to need for multiple sensors and processing systems
Solution Approach 1:
The patent creates a universal optical fiber sensing system that simultaneously performs multiple functions: measuring strain, measuring temperature, and enabling real-time monitoring. The same optical fibers and processing system handle all these tasks, improving productivity without proportionally increasing complexity through multi-functional integration.
Solution Approach 2:
The patent implements continuous real-time monitoring where optical fibers continuously measure strain and temperature during engine operation. The system maintains continuous data acquisition and processing without interruption, enabling ongoing validation and monitoring that improves productivity by eliminating downtime for manual measurement.
4Measurement precision
If optical fiber is used for strain measurement, then measurement precision is improved, but device complexity increases due to need for temperature compensation
Solution Approach 1:
The patent embeds temperature compensation within the existing optical fiber measurement system by nesting temperature sensors and unrestrained fibers alongside the strain-measuring fibers. The compensation logic is nested within the data processing algorithms, allowing precise strain measurement while managing complexity through hierarchical integration.
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
This approach provides accurate, real-time measurements of engine housing displacement and temperature, overcoming the limitations of traditional methods by distinguishing between strain and temperature effects, thus enhancing engine validation and operational monitoring.
Implementation Method 1
Known optical frequency domain reflectometry (OFDR) systems, such as shown in FIG. 1, based on Rayleigh scattering in optical fiber OF
Implementation Method 2
Thermal and mechanical effects on the fiber induce a frequency shift of the backscattered light that is proportional to the applied strain or temperature because fiber length varies with either application of strain or heat
Implementation Method 3
Temperature influence on the measured localized strain variances is accounted for by obtaining temperature measurements from a temperature sensor coupled to the housing
Data Source
AI summary
Operational gas turbine engine housing or casing dynamic strain, temporary or permanent displacement and/or temperature is measured by a distributed fiber optic sensing system (DFOSS) utilizing optical frequency domain reflectometry (OFDR) that is coupled to the turbine engine housing. The DFOSS/OFDR system measures localized variances in strain along the length of an optical fiber (OF), which are correlated with turbine engine housing displacement. Temperature influence on the measured localized strain variances is accounted for by obtaining temperature information from an another measurement system or by taking the same type OFDR measurements on unrestrained optical fiber (OF) and deriving compensated strain measurements that are not temperature influenced. The derived strain measurements along the DFOSS are correlated with housing displacement. Other embodiments include separate displacement measuring modules, each including DFOSS optical fibers, coupled along the engine housing.