The objective of this project was further development, laboratory validation, and demonstration of a microwave clearance measurement system (MCMS) on a SAGE4 GTF demonstrator engine. The system measured radial running clearances and axial rotor displacements in the low-pressure turbine with the goal of application in a closed-loop Active Clearance Control (ACC) system.
The project first developed measurement concepts in a laboratory setting, translate these concepts to designs suitable for implementation in the demonstrator engine and then test the measurement system during an engine test. In addition, the project demonstrated high operational reliability and field-replaceability of microwave sensors in the harsh low-pressure turbine environment with the goal of at least one typical engine maintenance interval. Finally, the accuracy of the measurement of radial clearance and axial position, measurement interval, measurement signal processing and data formats was demonstrated suitable for integration with an ACC system.
Successful validation of a reliable MCMS used in conjunction with a closed-loop ACC control system for aerospace gas turbine engines resulted in more efficient turbine and better engine performance and efficiency and hence improved fuel consumption and reduced emissions and will facilitate the early introduction of innovative and competitive European products into the market.
European aeronautics industry commitment (ACARE 2020 vision) is a result of the major concern in the 2000s to change the situation with the greenhouse gas effects, mostly due to CO2 emissions, resulting in the objectives to:
- Reduce fuel consumption and CO2 emissions by 50% (15-20% for the engine alone) per passenger kilometre;
- Reduce perceived external noise by 50%;
- Reduce NOx emissions by 80%.
The work performed within the scope of the MICMEST project contributes to these efficiency and environmental improvements by developing the technology readiness level (TRL) of the Microwave Clearance Measurement System (MCMS). The validation of an accurate and reliable microwave-based measurement system of radial running clearances and axial rotor displacements in the low-pressure turbine of an aeroengine could significantly contribute to improvement of efficiency of aviation gas turbine engines.
The objective of MICMEST project was further development, laboratory validation and demonstration of the MCMS on the Geared Turbofan Sustainable and Green Engine Demonstrator (SAGE4). The project led to the following major accomplishments:
- New blade shrouds including geometric features located on the tip of the shrouded blade were studied, designed and tested to provide an exploitable signal over a large range of axial position and radial clearance.
- A new spin rig was designed and built for the calibration and validation of the measurement system at system level in a realistic turbine casing environment in laboratory model before installation in the SAGE4 engine demonstrator.
- A sensor installation concept that meets SAGE4 demonstrator engine mounting requirements and containment constraints was designed and validated, enabling the installation of the sensors in SAGE4 demonstrator for the engine test
- The durability of the microwave sensors was demonstrated through a comprehensive laboratory temperature test campaign.
- The MCMS went through the entire SAGE4 engine test campaign. All along the testing phase the system proved able to record measurements data with no sensor failures. In addition, no degradation of the microwave sensors signal has been observed throughout the engine test campaign.
However, there are still some remaining technology gaps to be addressed and solved before the ultimate objective of a suitable microwave system as part of an Active Clearance Control (AAC) system for series application and capability of flying. In light of the engine test results, the gaps that have been identified show that the system cannot be considered as fully validated in the engine environment is therefore not suitable for being used in production low pressure turbines in the configuration of SAGE4 engine.
The system calibration is the major gap of the methodology at present. Establishing an accurate physical model of the measurement appears the best way to get confidence on the accuracy of the method. Various improvements can also be foreseen to make more robust, general and reliable the clearance measurement process.