Case-Integrated Cooled Tip Clearance Sensing for Gas Turbines
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Solution Overview
Problem
The movement of blade tips relative to the turbine case due to centrifugal forces and temperature changes leads to clearance variations, allowing combustion products to escape, resulting in performance loss in gas turbine engines.
Innovation Solution
A cooled tip clearance measurement system is integrated into the turbine assembly, featuring an annular cooling plenum and a tip clearance sensor housed within, with cooling air supplied to maintain sensor temperature below combustion products, and housing stand-offs to create an air gap for convective cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the turbine case is designed to minimize clearance between blade tips and blade tracks, then combustion product leakage is reduced and performance is improved, but the sensor housing will be exposed to high temperatures from combustion products
Solution Approach 1:
The turbine case is segmented into an inner case defining the gas path and an outer case spaced radially outward, creating an annular cooling plenum between them. This segmentation allows the sensor housing to be positioned in the cooler plenum region while the inner case maintains minimal clearance for performance.
Solution Approach 2:
The annular cooling plenum acts as an intermediary thermal zone between the hot combustion gas path and the sensor housing. Cooling air is introduced into this plenum to create a thermal buffer, protecting the sensor from high temperatures while allowing the inner case to maintain optimal clearance configuration.
2Measurement precision
If the tip clearance sensor is placed in close proximity to the inner case to accurately monitor tip clearance, then measurement precision is improved, but the sensor housing will be exposed to high temperatures from combustion products
Solution Approach 1:
The annular cooling plenum filled with cooling air serves as a thermal intermediary between the hot inner case and the sensor housing. This allows the sensor to be positioned radially outward of the gas path for accurate measurement while being thermally protected by the cooling air in the plenum.
Solution Approach 2:
The cooling air is locally introduced into the annular plenum specifically at the sensor housing location, creating a localized cool zone. This allows the sensor to operate in a cool environment while the rest of the turbine operates at high temperatures for performance.
3Measurement precision
If cooling air is supplied to the annular plenum to cool the sensor housing, then sensor temperature is reduced and measurement accuracy is maintained, but device complexity increases
Solution Approach 1:
The annular plenum between the inner and outer cases serves multiple functions: it provides structural support as part of the turbine case, creates a thermal barrier to protect the sensor, and serves as a channel for cooling air distribution. This multi-functionality reduces overall system complexity despite adding cooling capability.
Solution Approach 2:
The cooling air system is integrated with the existing turbine air supply, using air that is already available in the engine airflow path. The plenum structure itself serves as the cooling air distribution channel, eliminating the need for separate complex cooling ducts and valves.
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
The system effectively monitors and maintains optimal tip clearance, enhancing gas turbine engine performance by preventing combustion product leakage and ensuring accurate sensor readings.
Implementation Method 1
The annular cooling plenum may be configured to be flooded with cooling air at a temperature lower than a temperature of the combustion products
Implementation Method 2
transfer heat from the sensor to the cooling air so as to cool the sensor
Implementation Method 3
The plurality of stand-offs may extend from the radially-inwardly facing surface of the sensor housing and engage the inner case to space the radially-inwardly facing surface apart from the inner case to define a gap therebetween. The gap may allow the flow of cooling air to flow between the inner case and at least a portion of the radially-inwardly facing surface of the sensor housing.
Data Source
AI summary
A turbine assembly includes a bladed rotor mounted for rotation about an axis of the gas turbine engine, a case assembly, and a tip clearance system. The tip clearance system includes a tip clearance sensor located in an annular plenum defined between an inner case and an outer case included in the case assembly. The tip sensor is configured to monitor a tip clearance formed between the bladed rotor and the case assembly during operation of the gas turbine engine.