Non-contact Blade Tip Clearance Measurement in Turbines
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Solution Overview
Problem
Current methods for measuring blade tip clearance in gas turbines are time-consuming, require skilled technicians, and lack accuracy and reproducibility, especially when trying to determine individual blade clearances in fully assembled engines without disassembling the turbine.
Innovation Solution
A non-contact, radially oriented displacement sensor probe is mounted in an existing inspection port, allowing for real-time, sequential sampling of blade-tip clearance readings while the engine is in turning gear mode or with individual blades stationary, providing higher resolution and accuracy by determining the actual radial distance between the probe and the blade tip, and calculating the tip-gap by subtracting known distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical dial indicator is used for blade tip clearance measurement, then measurement can be obtained, but measurement precision and repeatability are poor due to subjective reading and technician skill dependency
Solution Approach 1:
The patent replaces the mechanical dial indicator system with a non-contact optical measurement system. The optical sensor captures images of the blade tip, and automated image processing algorithms determine clearance measurements, eliminating the need for manual reading of mechanical indicators and removing technician skill dependency.
Solution Approach 2:
The patent creates a visual copy (image) of the blade tip using an optical sensor, then analyzes this copy through automated image processing to determine clearance. This allows multiple measurements to be taken from the same visual record, improving repeatability and eliminating subjective interpretation of mechanical indicator readings.
2Ease of operation
If half shell measurement method is used by removing upper casing, then blade tip clearance can be measured, but measurement accuracy deteriorates because lower case changes shape without upper case support
Solution Approach 1:
The patent performs measurements while the engine casing remains fully assembled and supported, eliminating the need to remove the upper casing. By conducting the measurement in the preliminary state (fully assembled), the casing maintains its proper shape and structural integrity, ensuring measurement accuracy.
Solution Approach 2:
The patent uses non-contact optical measurement to access blade tip clearance information without requiring physical access that would necessitate casing removal. The optical sensor can measure through the inspection port while the casing remains intact, avoiding the structural changes that occur during half-shell measurement.
3Productivity
If mechanical dial indicator is used in turning gear mode, then maximum-minimum clearance range can be obtained, but individual blade clearance cannot be determined and measurement is time-consuming
Solution Approach 1:
The patent captures visual copies (images) of each blade tip as they pass through the measurement field of view. By recording images of individual blades in sequence, the system preserves information about each specific blade's clearance while maintaining efficient continuous measurement during rotor rotation.
Solution Approach 2:
The patent uses automated image processing feedback to identify and measure each blade tip individually as it passes the sensor. The system processes images in real-time, automatically determining which blade is being measured and recording individual clearance values, eliminating the need for manual intervention to obtain individual blade data.
4Measurement precision
If sequential manual measurement of individual blades is performed, then individual blade tip clearance can be determined, but measurement time increases significantly and errors occur if dial indicator alignment is not precise
Solution Approach 1:
The patent replaces the sequential manual measurement process with a continuous non-contact optical measurement system. The optical sensor automatically captures images of each blade tip as it passes through the field of view, and automated image processing determines individual clearances without requiring manual repositioning or alignment adjustments, significantly reducing measurement time while maintaining precision.
Solution Approach 2:
The patent enables continuous measurement of all blade tips as the rotor rotates, rather than requiring sequential stop-and-measure operations. The optical sensor continuously captures blade tip images during rotation, and automated processing extracts individual clearance data from the continuous stream of images, eliminating idle time between measurements.
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 method enables precise, repeatable, and efficient measurement of individual blade tip clearances with higher accuracy and resolution compared to traditional mechanical dial indicator techniques, reducing errors and improving measurement consistency across different technicians and measurement times.
Implementation Method 1
A non-contact, radially oriented displacement sensor probe is mounted in an existing inspection port
Data Source
AI summary
Turbine blade-tip clearance is measured in a fully assembled turbine casing by mounting a probe tip of a non-contact displacement probe in an inspection port of a vane cavity at a known distance relative to the inner circumferential surface of the corresponding ring segment. The displacement probe generates displacement samples that are indicative of probe tip distance from the turbine blade tip. Variations in probe distance data are recorded as the blade circumferentially sweeps the turbine casing. A data processing system correlates the distance data with localized blade-tip clearance gap. In some embodiments, blade rotational position data are collected by a rotational position sensor. In those embodiments, the data processing system correlates the distance and rotational position data with localized blade tip gap at angular positions about the turbine casing circumference.